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Next to the regular or weak verbs, Frisian has quite a number of irregular verbs. These could be divided into four groups, although the division is not without intersections.
Most irregular verbs can be characterized as strong. Their main feature is ablaut. As a result of this historical event, the vowel of the stem varies: the past tense and/or past participle may show a different vowel than the infinitive. This is different from the regular weak verbs where the vowel of the stem remains constant. An example of a strong verb is the verb slute to close, which has /y/ in the stem. Its past tense is sleat, with /I.ə/; the past participle is sletten, with /ɛ/. The vowel alternation is sufficient to indicate the past tense, and hence we see that the strong verbs lack the suffixes of the weak verbs which do mark them. Instead of the suffixes for the past participle (-d/-t for class I, -e for class II), we see the suffix -en as a second main feature of the strong verbs. An example is the participle sletten closed, which can be analyzed as slet-en.
Frisian also has weak verbs that are nevertheless irregular in that they show stem allomorphy. Irregularity emerged after historical phonological processes that affected a part of the paradigm. An example is meitsje to make. In Old Frisian this was makia, in those days fully regular (as for instance Dutch maken is still a regular weak verb). The /i/ (or maybe later /j/) of the ending caused palatalization, both of the preceding consonant /k/ and the stem vowel. The result is an infinitive form meitsje, and a present tense paradigm which runs as follows: (ik) meitsje I make - (do) makkest you make - (hy) makket he makes and (wy/jimme/hja) meitsje (we/you/they) make. The past tense makke and the past participle makke are regular, at least in the light of the Old Frisian forms. If, on the other hand, we were to take the infinitive meitsje and its putative derived stem meits- as point of departure, these forms would be irregular. Meitsje is a verb belonging to class II of the weak verbs. Another subgroup in this class displays an alternation /j~g/, for instance in the opposition jei vs. jage in the present versus past tense of the first person singular of the verb jeie to hunt. Furthermore, we find several weak verbs of class I that partially underwent a historical phonological shortening, which succeeded in a paradigm which is comparatively irregular. An example is the verb briede to roast, with its first person double ik bried I roast.PRES vs. ik brette I roast.PRET.
A third group of irregular verbs consists of auxiliary verbs. As in other languages, the most irregular verb is wêze to be. Another important category are the modal verbs, former preterite-present verbs. A characteristic feature is that they do not show a suffix -t in the third person present tense. So English 'he can' is Frisian hy kin, and not *hy kint.
Monosyllabic verbs constitute a fourth irregular category. Their infinitive lacks an ending -e or -je. Moreover, these verbs often show different stems. The verb sjen to see, for instance, has a present tense on the basis of the stem sjoch-.
A minor irregular subgroup consists of the verbs sizze to say and lizze to lay. Their irregularity is also caused by historical palatalization processes. Finally, a minor group of verbs shows irregularity in the present tense in that the vowel of the form of the second and third person of the singular is shortened (and often lowered). An example is the verb bite to bite, which has /i/, where its second and third person show /I/. This alternation is obsolete nowadays, but it still occurs in the dialect of the island of Schiermonnikoog.
Next to their inherent irregularity, strong and irregular verbs may display other peculiarities as well. For instance, auxiliary and monosyllabic verbs may have shortened forms, dealt with below in the section on apocope. An example is the present tense stem doch- of the verb dwaan to do, which may drop the final fricative, becoming do-. We also see developments with respect to the suffixal endings. One is the result of a historical rule of metathesis, which affected the past plural suffix -en. The order -ne can still be found after certain stems ending in a vowel, as described in past tense stems ending in a vowel. The plural past tense of the verb hawwe to have, for instance, is hie-ne, and not something like *hie-en. We also see attempts to make the endings more transparent. One can be located in the west of the language area, where strong participles that have absorbed the ending -en in the stem are augmented with a suffix -d, probably transferred from the weak verbs of class I. Thus the past participle dien of the verb dwaan to do surfaces as diend in these dialects. A relatively new development is the reinforcement of the ending -st of the second person singular of the past tense. This may turn into -est by insertion of a schwa. For instance, we get the form do tochtest you thought, which was do tochtst before.
As might be expected, there is pressure to reduce irregularity. Levelling occurs at various places. In particular, deviating forms in the present and past tense are vulnerable.
Finally, this topic also contains lists of strong and irregular verbs.
- Strong verbs
- Inflectional forms of strong verbs
- Irregular weak verbs belonging to class II
- Irregular weak verbs belonging to class I
- The verbs sizze to say and lizze to lie; to lay
- Auxiliary verbs
- Monosyllabic verbs
- Apocope
- Past tense stems ending in a vowel
- Developments with respect to the ending of the strong past participle
- Reinforcement in the past tense of the forms of the second person
- Shortening in the present tense
- Levelling
- List of strong verbs
- List of irregular verbs
As the other Germanic languages, Frisian has a considerable number of verbs, more than 100, that originate in the Germanic ablaut system. They lack the dental suffixes that build the preterite and the past participle. Instead, the stem of one or both of these categories displays a different vowel. An example is slute to close. Its preterite is sleat, and sletten is the form of the past participle. A total of three different vowels is rather rare, however. Thus the vowel of the infinitive may return in one of the other forms, for instance ride-ried-riden to ride, with a deviating preterite. Or, as is often the case, preterite and past participle display the same vowel, as in skinke-skonk-skonken to give, to pour.
A second feature of strong verbs is the ending of the past participle, which is -en, as may be seen in the examples above. In various cases, this ending is less conspicuous in that it is integrated in the stem syllable. If this is the case, the schwa of the suffix deleted. Examples are bedoarn spoiled, bleaun remained, bûn tied and sean cooked. The ending -en may even be the only indication that a verb is strong, at least historically. This is the case with the participle laden loaded, from the infinitive lade to load, which has a weak past tense lade loaded.
A few strong verbs also show variation in their consonantism, due to historical phonological processes. The verb sjitte-skeat-sketten to shoot has a deviating onset in the infinitive and present tense, as a result of palatalization before a high front vowel; in Old Frisian the infinitive was skiata. Palatalization also yields a different onset in the verbs jitte to pour, ferjitte to forget and jilde to cost, be valid (cf. English yield). Compare, for instance, the preterite geat and the past participle getten with the infinitival form jitte. Apart from the prefix, ferjitte to forget displays the same forms. The verb jilde has the non-palatalized form gou as a preterite. The verb sjonge-song-songen to sing has a similar onset as sjitte to shoot, but here as a result of some form of Old Frisian breaking (see Boutkan (1998). Something comparable has affected the first member of the triple fjochtsje-focht-fochten to fight.
Furthermore, a couple of verbs with an infinitive stem ending in /k/ show palatalization and assibilation in the past participle (which must have occurred in a period in which the following ending had a front vowel; cf. older spellings like -in). This concerns the participles brutsen (from brekke to break), dutsen (from dekke to cover), lutsen (from lûke to pull), rutsen (from rekke to stretch), sprutsen (from sprekke to speak), stutsen (from stekke to stick), strutsen (from strike to iron) and trutsen (from trekke to pull). Around the year 1600 the form baetsen still occurred, from bakke to bake, a verb that later turned to the weak class in its entirety. In the first time after this palatalization, the original final /k/ remained intact in the preterite, but later, especially in the south, the preterite forms of all of the members of this cluster took over the rhyme of the stem form of the past participle. For instance, for many speakers in the north the verb brekke to break still has the pattern brekke-briek-brutsen, but in the south this is generally replaced by brekke-bruts-brutsen.
Palatalization effects can also be observed at the end of the stem of the verbs sizze to say and lizze to lay, this time affecting the voiced velar consonant. It resulted, for instance, in a fricative /z/ in the infinitive (via intermediate /dz/), and in /j/ in some other forms. This resulted, among others, in the triple sizze say.INF to say, sei said.1SG.PRET /saj/ and sein said.PP /sajn/. Synchronically, no phonological relation between these various sounds exists anymore. As these verbs are originally weak, and moreover show other peculiarities, they will be dealt with in the verbs sizze en lizze in a separate section below.
A few verbs show a peculiar behaviour. On the one hand, they show vowel alternation, which points to their being strong. This idea might be reinforced by the fact that the past tense and past participle even show an extra consonant, i.e. /χ/. An example is bringe to bring, which has the form brocht brought both as past tense and past participle. Here is an overview of the verbs that have the same pattern:
| Infinitive | 1/3SG.PRET | Participle | Translation |
| bringe | brocht | brocht | bring |
| keapje | kocht | kocht | buy |
| sykje | socht | socht | seek |
| tinke | tocht | tocht | think |
Next to the unexpected final cluster /ɣt/ we also find a deviating final cluster /st/ in wist, the preterite of witte to know, and in doarst, one of the forms of the past tense and the past participle of doare dare. For the latter, see also the section on auxiliary verbs.
Scattered remnants of Verner's law may be found in variation in the coda of the verbs frieze to freeze and ferlieze to lose. They have as preterite the forms frear and ferlear, in which /z/ turned to /r/.
An alphabetical list of the Frisian strong verbs is offered in the List of strong verbs below.
The traditional division of the strong verbs is along the lines of the original seven Germanic ablaut classes. Since it has become muddled in the later development by all kinds of analogies, this division is given up by modern grammarians. As is also done in the list of strong verbs, they confine themselves to an alphabetical list. Examples are Hoekema (1996:54-69), Tiersma (1999:77-82), Eisma and Popkema (2004) and Popkema (2006:331-342). The traditional division can still be found in Sipma (1913:71-74) and, with direct references to the situation in Old Frisian, in Sipma (1949:31-36). Also with respect to the dialects on the island of Terschelling: Knop (1938). A mixed sytem is offered by Fokkema (1967:70-74). Van Blom (1889:144-154) and Sytstra and Hof (1925:141-147) have extended the division to eleven classes, mainly along the criterion of rhyming.
Kalma (1938:7-8) mentions the strong palatalized form baetsen baked. A recent treatment of the historical development of Frisian strong verbs is offered by Strik (2015).
Strong verbs do not deviate from weak verbs in their inflection of the present tense. As for an infinitive ending in -e or -je, they follow the rules as presented in weak verbs for class I and class II weak verbs. Likewise, the forms for the imperative, present participle and infinitive II need no extra attention, as they also follow the rules for weak verbs. Hence, the present tense has the endings -, -st and -t for the three persons singular, and the plural suffix is -e for most strong verbs. For the verb fine to find we then get ik fyn I find, do fynst you find, hy fynt he finds and wy/jimme/hja fine. This is exactly the same pattern that we find with class I verbs. Only a few strong verbs, displaying an infinitive ending in -je, appear to go along with the weak verbs of class II. These are bergje to store, fergje to require, hingje to hang, lykje to appear, terskje to thresh, tingje to haggle and waskje to wash. The present tense of these verbs follows the rules for the weak verbs of class II. To be concrete, for hingje to hang we then get for the present tense: ik hingje I hang, do hingest you hang, hy hinget he hangs and wy/jimme/hja hingje we/you/they hang. Furthermore, the present participle is hingjende and the imperative is hingje.
At first sight, there seems to be a difference for the past tense. Next to the vowel change in the stem, there is the following inflectional pattern:
| Number | Person | Suffix |
| SG | - | |
| 1 | -st | |
| 2 | - | |
| 2 polite | -en | |
| 3 | - | |
| PL | ||
| 1 | -en | |
| 2 | -en | |
| 3 | -en |
The suffixes represent person and number. A comparison reveals, however, that if we abstract away from the past tense markers -e/-de for class I or -e for class II, these endings are similar to what we see with the past tense of weak verbs. Likewise, one may observe the longer suffix -ste for the second person singular, for instance in the form do naamste you took.
It should be noted that the inflectional pattern for the past tense is the same in all cases, irrespective of the infinitive ending in -e or -je. A verb like hingje to hang shows the following preterite forms: ik hong I hung, do hongst you hung, hy hong he hung and wy/jimme/hja hongen we/you/they hung. The past tense suffixes of class II are not added, so we do not have *ik honge or *do hongest or *hy honge. And the past participle is prototypically hongen, and not a *honge or even *hongene.
It is worth mentioning that in the older language (18th/19th century) also a longer past plural ending -ene occurred. Probably, this was the result of a metathesis rule which turned -en to -ne, with the subsequent insertion of a schwa. Relics of this metathesis can still be found in a small set of verbs with a past tense stem ending in a centralizing diphthong, see past tense stems ending in a vowel.
The existence of the ending -ene was first noticed in Dyk (1996). That such endings are the result of metathesis is argued for Hoekstra (2008).
Next to the strong verbs, there is a group of verbs displaying different vowels in the past tense and the past participle as well. However, their past participle does not end in -en but rather in a form familar from the weak verbs. In fact, these verbs are weak. They do not belong to the set of traditional strong verbs with ablaut. More specifically, their deviating vowels are the result of historical phonological processes. The two weak classes have their irregular verbs. In class I, shortening has applied. The irregular forms of class II are the result of palatalization of a velar final consonant of the stem.
For the irregular verbs of class II we have to differentiate between stems ending in the voiceless velar stop /k/ and those which have a voiced velar fricative /ɣ/ as final segment. The former, combined with /j/ of the verbal suffix -je, end in a cluster /tsj/ after palatalization. A side effect of this palatalization is that the vowel turns to a diphthong ending in /j/. That change only applies before the suffix -je. This implies that only the infinitive, the first person singular and the three persons plural of the present tense, the present participle and the imperative are affected. For the verb meitsje to make, for example, we thus get the following paradigm for the present and past tense:
| Tense | Number | Person | Form |
| present | |||
| SG | |||
| 1 | meitsje | ||
| 2 | makkest | ||
| 2 polite | meitsje | ||
| 3 | makket | ||
| PL | |||
| 1 | meitsje | ||
| 2 | meitsje | ||
| 3 | meitsje | ||
| past | |||
| SG | |||
| 1 | makke | ||
| 2 | makkest | ||
| 2 polite | makken | ||
| 3 | makke | ||
| PL | |||
| 1 | makken | ||
| 2 | makken | ||
| 3 | makken |
The irregular weak verbs with a stem ending in /k/ are the following:
| Infinitive | 3SG.PRET | Translation |
| koaitsje | kôke | cook; boil |
| laitsje | lake | laugh |
| meitsje | makke | make |
| ploaitsje | plôke | pluck |
| reitsje | rekke;rakke | get; hit |
| smeitsje | smakke | taste |
| weitsje | wekke | watch |
The palatalization of /k/ never took place in the dialect of Hindeloopen. Of the verbs in the table above, Blom (1981) mentions the forms kòkje, lakje, meikje, plòkje, reikje, smeikje and wekje. It may also be the case that this extended to some verbs in other southern dialects. Southwestern forms like kokje, plokje and wekje are possible kandidates. In the Schiermonnikoog dialect, some of the verbs above did not palatalize either, as seen in lakje to laugh and plokje to pluck. In the other verbs, as is generally the case in this dialect, we do not see assibilation. So, verbs like katje to cook or metje to make are without an intermediate /s/.
| Tense | Number | Person | Form |
| present | |||
| SG | |||
| 1 | jei | ||
| 2 | jagest | ||
| 2 polite | jeie | ||
| 3 | jaget | ||
| PL | |||
| 1 | jeie | ||
| 2 | jeie | ||
| 3 | jeie | ||
| past | |||
| SG | |||
| 1 | jage | ||
| 2 | jagest | ||
| 2 polite | jagen | ||
| 3 | jage | ||
| PL | |||
| 1 | jagen | ||
| 2 | jagen | ||
| 3 | jagen |
The irregular weak verbs with a stem historically ending in /ɣ/ are the following:
| Infinitive | 3SG.PRET | Translation |
| feie | fage | sweep |
| jeie | jage | hunt |
| kleie | klage | complain |
| koaie | kôge | chew |
| krije | krige | get |
| loeie | loege | pile |
| ploeie | ploege | plough |
| toaie | tôge | carry |
It remains to be investigated whether there have been more members of this group. A possible candidate is the verb druie to dry, which exists next to droegje. The latter seems to be a direct conversion of the adjective droech dry. The first could be a product of palatalization, although it must be admitted that the verb nowadays belongs to the regular weak class I. A comparable pair is kluie to gnaw next to kloegje, both forms being fairly obsolete. For the tendency of these palatalization verbs to convert to class I, see the section on schwa deletion below.
Another possible candidate is boeie to turn a horse to the right, which might be connected to bûgje to bow, although, according to Dyk (1984-2011) this verb is regularly inflected as a member of the weak class I.
| Present tense | Translation |
| ik krij | I get |
| do krijst | you get |
| hy krijt | he gets |
| wy/jimme/hja krije | we/you/they get |
A peculiar feature of this second group of irregular weak verbs of class II is the deletion of the final schwa both in the first person of the present tense and in the imperative. We have ik krij I get and the imperative krij!. However, we do not see *ik krije or *krije!, although these would be the forms expected if the verb follows the paradigm of class II verbs in a regular manner. This could be an indication that the form of the Frisian imperative is rather based on the form of the first person instead of the stem (for this issue, see also categories and also the imperatives of the category of monosyllabic verbs).
A possible explanation might be found in the phonology. In the normal case, class II verbs never occur with a stem ending in a vowel. Instead, we find -je only after a consonant. If, then, the final schwa deletes, this will always result in a final cluster -Cj, which is intolerable in the phonotactics of Frisian. Only here, where /j/ happens to follow a vowel as the accidental effect of palatalization, we happen to meet the suitable context for the deletion of the final schwa.
The circumstance of schwa deletion in the first person of the present tense might have the further effect of levelling in the present tense. The first person form krij might be reinterpreted as a form of the weak class II, which also lacks an ending after the stem. This could be reinforced by the form of the present plural, which is krije. Analyzed as a class II verb, this would be krij-je. However, phonetically there is no objection against the analysis krij-e. The pronunciation is similar, but in the latter case the verb would be a member of class I. If so, it is conceivable that the two remaining forms would also turn to class I. This would result in the second person singular krijst (analyzed as krij-st) and the third person singular krijt (< krij-t), which are the actual forms for many speakers. (For a comparable effect in the realm of conversion verbs, see Hoekstra (1998:152)).
As stated above, weak verbs of class I may become irregular as a result of a historical shortening in a part of the paradigm. In fact, we see that the non-affected members are subjected to other sound changes, so that the difference within the paradigm even increases. With respect to irregular class I verbs, there are three subtypes. One has a shortening resulting in /ɛ/, another in /a:/ (after a subsequent compensatory lengthening, see Spenter (1968:16)), and finally we have a change resulting in /I/. From a historical perspective the distribution within the paradigm is the opposite of what we saw with the irregular weak verbs of class II. That is, those members of the paradigm that remained stable in class II are typically affected by the sound change in class II. The overall effect is that we find an equal distribution of the allomorphs, but in class I we typically see effects in the second and third person of the present tense, the whole of the past tense and the past participle. Here is a paradigm of the verb bliede to bleed, which belongs to the first subtype:
| Tense | Number | Person | Form |
| present | |||
| SG | |||
| 1 | blied | ||
| 2 | bletst | ||
| 3 | blet | ||
| PL | bliede | ||
| past | |||
| SG | |||
| 1 | blette | ||
| 2 | blettest | ||
| 3 | blette | ||
| PL | bletten | ||
| infinitive I | bliede | ||
| infinitive II | blieden | ||
| present participle | bliedende | ||
| imperative | blied |
| Infinitive | 3SG.PRET | Translation |
| bliede | blette | bleed |
| briede | brette | roast |
| fertriette | fertrette | vex |
| fiede | fette | feed |
| liede | lette | ring |
| moete | mette | meet |
| rêde | rette | save |
| riede | rette | guess |
| sliepe | slepte | sleep |
For the irregular weak verbs of class I showing long /a:/ as alternating vowel, we take spriede to spread as an example. Here is an abridged paradigm:
| Tense | Number | Person | Form |
| present | |||
| SG | |||
| 1 | spried | ||
| 2 | spraatst | ||
| 3 | spraat | ||
| PL | spriede | ||
| past | |||
| SG | |||
| 1 | sprate | ||
| 2 | spratest | ||
| 3 | sprate | ||
| PL | spraten | ||
| infinitive I | spriede | ||
| infinitive II | sprieden | ||
| past participle | spraat | ||
| present participle | spriedend(e) | ||
| imperative | spried |
| Infinitive | 3SG.PRET | Translation |
| deie | date | kill |
| liede | late | lead |
| skiede | skate | part |
| spriede | sprate | spread |
| stjitte | state | push |
The third subtype of the irregular weak verbs of class I only consists of one verb: lije to suffer. Its alternating vowel is /I/. The verb has the following paradigm:
| Tense | Number | Person | Form |
| present | |||
| SG | |||
| 1 | lij | ||
| 2 | litst | ||
| 3 | lit | ||
| PL | lije | ||
| past | |||
| SG | |||
| 1 | litte | ||
| 2 | littest | ||
| 3 | litte | ||
| PL | litten | ||
| infinitive I | lije | ||
| infinitive II | lijen | ||
| past participle | lit | ||
| present participle | lijend(e) | ||
| imperative | lij |
A good source for this section, apart from the usual grammars, is Hoekstra (1989). In particular, he calls attention to historical shortenings that have been levelled out nowadays. Sipma (1944) points to the existence of some doublets in the subtype with a preterite with /ɛ/. Many details about levelling effects can be found in Hof (1951). The deviating forms in the second and third person singular in the present tense are put in a comparative perspective in Dammel (2010).
In a sense, the verb pair sizze to say and lizze to lie; to lay resemble the verbs above. Originally, they had regular paradigms (although lizze is a merge of strong Old Frisian lidza to lie and the weak causative ledza to lay). Nowadays their present tense is irregular, also with the second and third person singular as deviating members with their stem sei-. However, the causing factor of the irregularity is not shortening but rather palatalization. Thus the final consonant /z/ of the stem siz- is a result of palatalization from Proto-Frisian seggia, via Old Frisian sedza, of which the stem vowel raised to Old Frisian sidza. Later, the consonant cluster /dz/ simplified to single /z/. In other contexts, the original /ɡ/ palatalized to /j/, resulting in the stem sei /saj/, although the verb leze to lay in the dialect of Schiermonnikoog still has preterite forms with a velar fricative.
The verbs sizze to say and lizze to lay are mainly strong nowadays, displaying the forms sei say.1/3SG.PRET and sein say.PP. However, an area in the northeast, the neighbouring island of Schiermonnikoog, and the dialect of Hindeloopen still have weak past participles in seid and leid, in the northeast also abbreviated to sei and lei.
Here is a paradigm of sizze; the verb lizze goes the same way:
| Tense | Number | Person | Form |
| present | |||
| SG | |||
| 1 | sis | ||
| 2 | seist | ||
| 3 | seit | ||
| PL | sizze | ||
| past | |||
| SG | |||
| 1 | sei | ||
| 2 | seist | ||
| 3 | sei | ||
| PL | seine(n) | ||
| infinitive I | sizze | ||
| infinitive II | sizzen | ||
| past participle | sein (seid) | ||
| present participle | sizzend(e) | ||
| imperative | sis |
It should be pointed out that these verbs were practically the first to develop a reinforcement of the ending in the second person singular of the past tense, to discriminate it from the similar form of the present tense. We then get the preterite seidest, as will be dealt with in reinforcement in the past tense of the forms of the second person.
The historical development of sizze to say is briefly described and presented in a comparative context in Nübling (1999:61). See also Nübling (2000). Hof (1933:174) has a map of the distribution of the forms of the past participle of sizze. For the data of Schiermonnikoog: Visser and Dyk (2002). For Hindeloopen: Blom (1981).
Traditionally, auxiliary verbs are divided into four categories: those for aspect (hawwe to have, wêze to be for the perfect), tense (sille will for the future), passive (wurde to be) and for modality. Especially the latter have some common characteristics.
As in other languages, the most irregular verb is wêze to be. It has four different stems. The stem of the infinitive also occurs in the present participle wêzend(e) and in the imperative wês. The vowel is shortened in the past participle west. Most forms of the present tense show a stem bin (which surfaces only partially in the second person bist). The form of the third person singular is is. Finally, the stem of the past tense is wie.
The imperative is wês. This would be a regular form if we derive the imperative as being similar to the stem of the infinitive. However, in this respect the verb wêze is exceptional: if the infinitive and the first person singular of the present tense appear to possess different stems, it is rather the form of the first person that is on the basis of the form of the imperative; see monosyllabic verbs for some data. The past participle of the verb deserves two remarks. First its form. It has a "weak" ending, spelled as -t). The Old Frisian strong form wesen only survived on the island of Schiermonnikoog as wein. In the southwest the form weest is coming up, probably under the influence of Dutch geweest. Secondly, the past participle west needs the auxiliary hawwe to have. This is equal to the situation in English, but different from Dutch and German, which take the auxiliary zijn and sein, respectively. Again under Dutch influence, many speakers of Frisian change to a form of wêze, nowadays.
For a dialectical map of the distribution of the forms west and weest, see Hof (1933:130). For the choice of the auxiliary, see Popkema (1984) and De Rooij (1988). Hoekstra and Wolf (2004) discuss the fact that the transition to a form of wêze as auxiliary of the participle west is hampered in more complex verbal clusters, in which the auxiliary emerges as an infinitive. They explain the aversion against the combination west wêze as an instance of a syntactic OCP-effect. For a historical account, both of the form of the participle and its auxiliary selection, see Johnston (1994).
About the auxiliaries hawwe to have and wurde there is less to say. The first is dialectically the most interesting of the two. Hawwe varies along the choice of the stem vowel, which is /ɛ/ in the south western half, and the final consonant of the stem. Varieties with /b/ occur in a broad strip in the southeast, with /v/ in the rest of the language area. Both hawwe and wurde are strong, although the preterite of the latter tends to weaken in the south. The past participle wurden has the form woarn in northeastern dialects. In more or less the same area the past participle is used in participial passive constructions, along with the situation in English and German. Thus English this has been washed is dit is wasken wurden/woarn in the northeastern dialects; compare also German dies is gewaschen worden. The rest of the Frisian language area is without this overt representation of the passive: dit is wosken. Compare this with Dutch dit is gewassen (*geworden). The passive participle may also optionally be deleted after a modal verb. Next to dit moat meand wurde this must mowed be this should be mowed we have also dit moat meand this must mowed.
On the four dialectical variants of the infinitive of hawwe, see the map in Hof (1933:70). Tamminga (1963:207-209) gives some morphological, syntactic and semantic data about wurde. The northeastern passive construction is briefly dealt with in Hoekema (1963).
A salient feature of many modal auxiliaries is the fact that they lack a suffix -t in the third person of the present tense. In this way the third person becomes similar to the first person. This is the case with the following verbal forms: kin can.3SC.PRS, mei may.3SG.PRS and wol want.3SG.PRS. The modal verb moatte must might be expected to show the same behaviour, but this cannot be verified as its stem already ends in [t] by itself. The verb doare dare also used to have doar dare.3SG.PRS, especially in northern and western clay area, but more and more this form tends to be replaced by regular doart. It seems that in the area where this verb shows breaking, the suffix -t is always obligatory. It should be noted that a present tense third person singular without -t can also be found with the verb doge to be right, although this is not an auxiliary. This form dooch will now be almost obsolete, however. For many speakers the verb kenne to know is formally merged with kinne, with the result that this verb may also show a third person without -t.
A deviating form for the second person in the present tense once existed in the older language. The modal verbs sille and wolle displayed a form without the suffix -st. The Renaissance poet Gysbert Japicx (1603-1666), for instance, had the forms sitte and wotte. These forms have only survived in the dialect of the island of Schiermonnikoog, as satte and wotte, respectively. The deletion of the stem final /l/ is not unusual is these verbs; see apocope for more information about this subject.
This suffix -te has not been studied separately in Frisian linguistics. For the Middle Dutch (13th century) ending -t, see Berteloot (1999). It appears that also in Middle Dutch the same two verbs, Dutch zullen and willen, are the most persistent ones in the retention of this special suffix.
Several modal verbs have the feature that they have two forms at their disposal for the past participle, often dialectically distributed. One is strong, with the suffix -en, the other weak with -d, or even irregular. Here is an overview:
| Infinitive | 3SG.PRES | Strong participle | Weak participle | Translation |
| doar(r)e | doar(t) | doar(r)en | doard/doarst | dare |
| hoege | hoecht | hoegen | hoegd | need |
| kinne | kin | kinnen | kind | can |
| meie | mei | meien | mocht | may |
| moatte | moat | moatten | must | |
| sille | sil | sillen | sild | shall/will |
| wolle | wol | wollen | wold | want |
A general description is Hoekstra (1992). He also pays attention to the infinitival complementation of these verbs (with or without the particle te). The participles ending in -en can easily mislead us in thinking that they are in fact infinitives. That such an assumption may lead to wrong conclusions is shown in Hoekstra (2010).
An auxiliary verb that belongs to the formal register is pliigje to be used to. It is defective as it has no past participle. The verb was weak in Old Frisian, but interestingly, its past tense is irregular nowadays: the forms placht- and plicht- not only show a vowel different from the infinitive, but also the addition of an extra /t/ to the stem. It is not fully clear where these forms come from. Placht- may be direct interference from Dutch. The shortening and lowering in plicht- reminds one of a comparable phenomenon, but that is restricted to the present tense, and only to infinitives ending in -e. It seems that the preterite form plicht- has been the basis of a variant verb plichtsje, which is fully regular.
On the diffuse semantics of the tenses of this verb, especially in Old Frisian, see Meijering (2003). Possibly, this unclear situation also was the basis of the development of the variant plichtsje.
There is another group of irregular verbs that is mostly referred to as "monosyllabic". As such, these verbs can be considered as strong: they show vowel change in the past tense and past participle, and the latter also ends in /n/. However, they display some additional features, which calls for a separate treatment. This group has the following members:
| Verb | Translation |
| dwaan | do |
| gean | go |
| jaan | give |
| sjen | see |
| slaan | hit |
| stean | stand |
| tsjen | set forth |
| (fleane) | fly |
Although the infinitive of fleane to fly is not monosyllabic, it does originally belong to this group, too. Anyway, the corresponding infinitival form fjain in the Schiermonnikoog dialect is definitely monosyllabic, and the Renaissance poet Gysbert Japicx (1603-1666) still had the monosyllabic form flean. Also, the dialect of Hindeloopen had an older form flên, next to modern flêne. The verb tsjen to set forth is restricted to the higher registers nowadays, and tends to become obsolete.
One conspicious feature of this group is the fact that its members have only one infinitival form at their disposal. Probably it is not monosyllabicity that is the causing factor here, but rather the fact that these verbs do not end in a schwa. Normally, the infinitive I ends in a schwa, either as the suffix -e or the suffix -je. For the infinitive II an /n/ is added. Indeed, we see this pattern also for the verb fleane, which has the form fleane as infinitive I and fleanen as infinitive II. But for the other members of this group only a single infinitival form is found. Compare:
Another feature of several members of this group is that they have a separate stem in the present tense. Mostly its rhyme is -och (or -uch in the clay area) for instance in the first person singular forms (ik) doch (from dwaan to do), (ik) sjoch (from sjen to see) and (ik) tsjoch (from tsjen to set forth). Note that in this feature fleane to fly with its form (ik) fljoch is in conformity with the other members of this group. Mostly, this stem with -och covers the whole present tense, for instance in the verb dwaan to do:
| Person | Form |
| 1 | doch |
| 2 | dochst |
| 3 | docht |
| PL | dogge |
The same can be observed with sjen to see and tsjen to set forth. The situation in fleane to fly is less straightforward. The grammar of Sytstra and Hof (1925:148), for example, mentions forms with -och only for the second and third person singular, but as an alternative also for the full paradigm of the present tense. On the other hand, quite some speakers have levelled into the other direction, so that the present tense does not show another stem and is regularly in accordance with the stem of the infinitive. We then get ik flean, do fleanst, etcetera.
A pattern with deviating stems for the second and third person singular can also be observed in the verbs gean, stean to stand and slaan to hit. Here is an overview of the present tense of these verbs:
| Infinitive | 1SG | 2SG | 3SG | Plural |
| gean | gean | giest | giet | geane |
| stean | stean | stiest | stiet | steane |
| slaan | slaan | slachst | slacht | slane |
There is a great deal of dialectical variation in these verbs, especially in gean and stean, some of which can be traced back to different infinitival forms in the Old Frisian period. On the other hand, the verb jaan has a stem jou- in the entire paradigm of the present tense. It should be noted, however, that this is the present-day situation. For earlier stages, Veen (1984-2011) mentions the stem jaan for the first person singular and for the plural.
Of those verbs in this group that show a different stem in the infinitive and the first person singular of the present tense, the imperative invariably opts for the latter, as can be seen in the following figure:
| Infinitive | 1SG.PRES | Imperative |
| dwaan | doch | doch |
| jaan | jou | jou |
| sjen | sjoch | sjoch |
| tsjen | tsjoch | tsjoch |
Dutch also has monosyllabic verbs ending in /n/, although the corresponding verbs of Frisian jaan to give and tsjen to set forth do not belong to the stock in Dutch. A more serious difference has a structural character. In Dutch, the final /n/ of the infinitive can be analysed as a suffix, comparable to the infinitival suffix -en, of which the schwa is deleted after the stem that ends in a vowel. If we view it in this way, the Dutch endings of these verbs are fully regular. In Frisian, on the other hand, the stem does not end in a vowel but rather has incorporated the final element /n/. In as far as the stem of the infinitive and the present tense are identical, we see regular endings, on the assumption that /n/ belongs to the stem. The first person singular then gets a zero ending, for instance (ik) gean (I) go of the verb gean to go. And the plural form of the present tense is geane, to be analysed as gean-e. For the Dutch facts, see monosyllabic verbs.
A detailed and comprehensive overview of historical and dialectical variation with respect to the verbs gean, stean and dwaan is offered by Hof (1946). He also gives the Old Frisian forms of these verbs; for the Old Frisian forms of the other verbs, see for instance Sytstra and Hof (1925:147-149). Middle Frisian forms, i.e. those of the poet Gysbert Japicx, can be found in Brandsma (1936). A historical treatment is also Kramer (1996). He also gives parallels in East and North Frisian dialects.
Not all items are pronounced exactly as they occur in the morphological paradigms described above. Especially in frequent forms we see reduction, which mostly boils down to some form of truncation of suffixes or even final parts of stems. For finite forms, only those of the present tense are affected. Reduction in infinitives and participles is relatively rare.
The deletion of a suffix is seen in the plural -e of the present tense. In fact, all auxiliary and the monosyllabic verbs show this behaviour, especially in more rapid speech. Quite common are forms like wy bin we are instead of wy binne, jim moat you (plural) must instead of jim moatte, or se gean they go instead of se geane. Many speakers delete -e in the paradigm of lexical verbs as well, especially before clitics, for instance in dan sitt' we te smoken then sit-we to smoke then we are smoking.
The dialect of the island of Schiermonnikoog lacks the suffix -t of the third person present tense singular in three irregular verbs, where the other dialects are regular in this respect. The forms gie go.3SG.PRS goes of the verb gain to go, stie stand.3SG.PRS stands of stain to stand and (optionally) sei say.3SG.PRS says of seze to say are involved. This deletion is probably quite old: Reyner Bogerman, the author of a collection of proverbs of the midst of the sixteenth century, also had the form ha have.3SG.PRS has of the verb hawwe to have. He originated from the mainland, but was from the same northeastern region. The deletion reminds one of the lack of -t in the third person of the present tense of the weak verbs of class II in the same dialect, as it is mentioned in the table above.
We also see truncation in the stem. For finite forms, this truncation is dependent on the quality of the final consonant, i.e. we see the process only with /ɣ/, /l/ and /v/. The following stems are involved:
| infinitive | translation | full stem | reduced form |
| dwaan | do | doch | do |
| fleane | fly | fljoch | fljo |
| hoege | need | hoech | hoe |
| sjen | see | sjoch | sjo |
| sille | will; shall | sil | si |
| wolle | want | wol | wo |
| hawwe | have | haw | ha |
| hoeve | need | hoef | hoe |
De verb hoege/hoeve need has two varieties, where hoege is more to be found in the northeast, and hoeve in the southwest. Both display a shortened stem, however. The verb hawwe to have has stems ending in /v/ and /b/, depending on the dialect, as we have seen in the section on auxiliary verbs. Those with /b/ are not involved in the reduction process.
Although the stem is reduced, we do see the full endings -st and -t of the second and third person, the latter only if this is applicable; hence -t is lacking in the verbs sille and wolle. The presence of an inflectional ending is different for the suffix -e of the plural persons: if the stem is truncated, this suffix is deleted as well. For a verb dogge to do, for example, this results in the following reduced forms:
| Number | Person | Full form | Reduced form |
| SG | |||
| 1 | doch | do | |
| 2 | dochst | dost | |
| 3 | docht | dot | |
| PL | dogge | do |
The reduced forms are not represented in the orthography, with the exception of the verb hawwe. However, the reduction itself is also different, in that the final consonant of the stem of this verb, whether it is /v/ or /b/, is never heard in the second and third person singular. Hence, these forms are invariably spelled as hast and hat, respectively. In addition, we see the spelling ha, which can correspond to the full form haw for the first person singular or full hawwe of the plural forms.
Before the clitics 'k I, we we, je you (polite) and jim you (plural), the verb moatte must shows reduction as well, in that the final /t/ of the stem may vanish. This may result in the sequence /mak/ next to moat ek must I. The verbs hâlde to keep and wurde to get show a similar behaviour. On the other hand, reduction of final /l/ of the verbs sille and wolle is not seen before the clitic er he, which significantly has an initial vowel. Hence, the sequence *wo er wants he is not heard; rather it is wol er.
The verb moatte must is special in that it shows a subject-object asymetry. That is, deletion of the stem-final /t/ only occurs bfore subject clitics. Before objects, it is retained:
The most extensive treatment of these reduction phenomena is Visser (1988:210-216). They have also been dealt with shortly in Tamminga (1963:145-148) and Tamminga (1985:121-123). The author rejects the habit of some younger writers to reflect the reduced forms in their spelling. A clear comparison with verbs that do not show such deletion is given by Veenstra (1994:121-124). An indication that shortened forms already existed in the 19th century is offered by Brouwer (1969:197). For an account of these phenomena from a phonological perspective, see verb stems with and without final consonant and shortened words in combination with clitics. See also (Meer 1986). A dialect map of both variants of the verb hoege/hoeve need can be found in Van der Veen et al. (2001:62).
Of the infinitival forms, we see only truncation in the infinitive I of hawwe to have, which often reduces to ha, the same form that also occurs as the reduced plural of the present tense. The infinitive II is usually the full form hawwen, although in some dialects of the northeast reduced ha exists as well, for instance as te ha to have instead of te hawwen.
If even infinitive II ends in a vowel, one may conclude that the stem of the verb is reanalyzed completely. Such a reanalysis will be the reason that in the same northeastern area, superficially speaking, a new stem has developed. For instance, one can hear a sequence like har ik have I there. Veenstra (1994) also mentions the forms dor (of the verb dwaan to do), sjor (of sjen to see) en slar (of slaan to beat). He considers /r/ a hiatus filler, in this particular Frisian case the result of rule inversion: R-deletion is normally prohibited before a vowel, and therefore this context might be favourable for R-insertion as well. See also Veenstra (1994).
The insertion of /r/ is different from stems with /ɣ/ (or possibly /χ/), which can be observed with some speakers and in some internet fora, where one may encounter sequences spelled as ik hach I have or wy hache we have. The emergence of such forms is possibly analogical, a kind of rule inversion of the apocope that we see in certain other irregular verbs; for the relevant forms see in the table above.
In the dialect of the island of Schiermonnikoog some more infinitives may be truncated. Next to ha from hawwe to have we also have lee from leze to lay, see from seze to say, wa from wazze to be and wè from wezze to get. According to the dialect's dictionary Visser and Dyk (2002), these shortened infinitives typically occur at the end of a sentence. This restriction, however, does not apply to mainland Frisian ha. Shortened infinitives may be found on an even larger scale in the mixed Dutch-Frisian rural dialect of the region Het Bildt in the northwest of the province. Examples are gee from geve to give, bly from blive to remain, hoe from hoege/hoeve need and mâ from mâge may. In this dialect, also finite forms are fairly often truncated. See Buwalda et al. (2013:xxxvi-xxxix) for a quick overview. As far as is known, all cases of truncation in these dialects apply to the infinitive I. Infinitive II, the one with the suffix -en, is not affected.
Verbs with a stem ending in a vowel, which boils down to ending in a diphthong, may show two peculiarities. Firstly, we see a deviating ending -ne in the plural of the past tense, instead of regular -en. An example is hie-ne had.PL. Furthermore, after such stems a /d/ may be inserted before the clitic form er he. Hence we get hied er had he next to hie er.
The ending -ne especially occurs after centralizing diphthongs. In the table below is an overview, the columns showing the stem, the past plural, the infinitive and a translation, respectively:
| Stem | Plural | Infinitive | Translation |
| die | diene | dwaan | do |
| gie | giene | gean | go |
| hie | hiene | hawwe | have |
| snie | sniene | snije | cut |
| stie | stiene | stean | stand |
| wie | wiene | wêze | be |
| koe | koene | kinne | can |
| soe | soene | sille | will |
| woe | woene | wolle | want |
| bea | beane | biede | offer |
| sea | seane | siede | boil |
In addition, we find the ending -ne in those dialects which have the diphthong /öə/ in the past tense of strong verbs with the pattern -iuwe in there infinitive, for instance the verbs bliuwe remain or skriuwe write. Such verbs may show plural past tense forms like bleaune or skreaune.
However, we see regular -en in those dialects which have a past tense stem ending in the semivowel /w/. For instance, in the south and east we have the plural past tense /bljɔwən], mostly spelled as bleauwen. This is in accordance with other past tense stems with a falling diphthong ending in /w/, like gou (from jilde apply) or stau (from stowe dash, rush, be dusty), which likewise show regular -en. Also the past stems ending in a falling diphthong with the semivowel /j/ are regular, however, with the exception of the verbs lizze lay; put and sizze say. These may show the plural past tense forms leine and seine, respectively.
Probably, the ending -ne can best be understood as a relict of an older metathesis, which turned original -en to -ne. This process affected the strong or irregular verbs ending in a consonant as well. In addition, a schwa was inserted between the final consonant of the stem and the element /nə/. Thus for a form like namene (from the verb nimme to take) we could assume a development namen > (with metathesis:) naamne > (with schwa insertion:) namene. Such endings in -ene disappeared in the course of the 19th century, thereby apparently dropping the final schwa, with the result that original -en reappeared. But in a number of the verbs the reversed order -ne remained, probably because the initial /n/ started to function as a hiatus filler between the final schwa element of the diphthong of the stem and the schwa of the ending. As a further development, we see that these formations ending in -ne analogically conform to the general pattern which demands that past tense forms end in a schwa plus /n/. As a result, we nowadays see a form hienen next to hiene, etc. What has remained, however, is the unexpected /n/ right after the stem hie-.
With respect to the set of verbs with an infinitive ending in -iuwe, some speakers went one step further in that they reanalyzed this /n/ as belonging to the stem. See the following table for what this means for a verb like skriuwe to write:
| Person singular | Standard | Reanalyzed |
| 1 | skreau | skreaun |
| 2 | skreaust | skreaunst |
| 3 | skreau | skreaun |
The fact that this set of verbs in particular could undergo this reanalysis may possibly be attributed to the circumstance that the new stem is similar to the form of the past participle, i.e. skreaun write.PP written. Of the other strong verbs, also biede offer with its past participle bean is known to show stem-final /n/: ik bean I offered etc.
The idea that the form -ne is a result of a metathesis rule has been put forward in Hoekstra (2008). Visser (1989) takes a synchronic view, and sees /n/ primarely as a hiatus filler. For a phonological perspective, see also the plural preterite of strong verbs. A lot of historical material can be found in Breuker (1993). Reanalyzed forms like ik bleaun I remained have been observed first by De Haan (1949). For historical and dialectical variation of the verbs with the patterm -iuwe, see Dyk (2002).
Verbs with a past tense stem ending in a vocalic segment show another peculiarity. They may optionally invoke the insertion of a segment /d/ before the third person singular masculine clitic er /ər/. Again, the verbs sizze to say and lizze lay join these verbs in this feature. In this way, we get formations like wie-d-er was he, woe-d-er wanted he or sei-d-er said he. As above, we may assume that /d/ has a function of a hiatus filler. Although /d/ is normally orthographically connected to the stem, for instance written as wied er, it cannot be part of the stem in a structural sense; in that case, voiced /d/ would have turned into voiceless /t/ before the clitic. Therefore, /d/ is possibly better connected to the clitic. The form der would then be a variant of er, but only occurring in quite specific circumstances. Note that we also find D-insertion before the same clitic er after stems ending in /r/, /l/ and /n/. For this issue, see the topic on D-insertion.
The stems discussed in this section still have another property: they can easily invoke reinforcement of the ending of the second person singular. For this topic, see reinforcement in the past tense of the forms of the second person.
The ending of the past participle of strong verbs is regularly -en. In Frisian, however, this ending may become integrated in the stem, with the effect that the schwa of the suffix is deleted, and, moreover, that the remaining /n/ is no longer part of a separate syllable. This historical event occurred with the following verbs:
| Infinitive | Translation | Participle |
| bedjerre | spoil | bedoarn |
| begjinne | begin | begûn |
| bidde | pray | bean |
| biede | offer | bean |
| bine | tie | bûn |
| bliuwe | stay | bleaun |
| driuwe | drift | dreaun |
| dwaan | do | dien |
| farre | sail | fearn |
| ferdjerre | ruin | ferdoarn |
| ferdwine | disappear | ferdwûn |
| ferlieze | lose | ferlern |
| fine | find | fûn |
| fleane | fly | flein |
| gean | go | gien |
| hawwe | have | hân |
| jaan | give | jûn |
| kliuwe | climb | kleaun |
| lizze | lie, lay | lein |
| priuwe | taste | preaun |
| rinne | walk | rûn |
| riuwe | lace, string | reaun |
| siede | cook | sean |
| sizze | say | sein |
| sjen | see | sjoen |
| skriuwe | write | skreaun |
| slaan | hit | slein |
| snije | cut | snien |
| spije | spit | spein |
| spinne | spin | spûn |
| stean | stand | stien |
| stjerre | die | stoarn |
| swije | be silent | swein |
| swine | disappear | swûn |
| triuwe | push | treaun |
| tsjen | go, proceed | tein |
| wine | wind | wûn |
| winne | win | wûn |
| wiuwe | wave | weaun |
| wriuwe | rub | wreaun |
In the western part of the language area, these reduced forms of the past participle are usually augmented by a segment /d/. This results in forms like bleaund stayed, diend done, hand had (with shortening of the vowel) or seind said. One may safely assume that the reason for this change is an attempt at making the participle more transparent, as the original suffix -en is absorbed in the stem. Moreover, in contrast to for instance German and Dutch, Frisian lacks a prefix ge- that marks the category of the past participle. The ending /d/ must have been transferred from the weak class I, which suffix of the past participle is likewise -d.
This doubling of the participle in order to create greater transparency is, in a certain sense, a mirror of what can be observed in the weak class I itself, where we see an addition of the "strong" ending -en after stems that end in /d/ or /t/. (See for that phenomenon weak verbs). However, it should be remarked that although the core of both changes lies in the west, the areas do not fully coincide: the combination of -d with strong participles is restricted to the west, indeed, where we may find -en with weak participles in a much wider area nowadays.
The participles in the table above all end in -n. Therefore we could maintain that a remnant of the original ending -en still survives. This is different with some verbs ending in the other nasals, /m/ and /ŋ/. A comparable deletion process may be observed after stems ending in these nasal consonants. The difference is that in this case nothing of an alveolar nasal is left behind. Here is an overview of relevant verbs:
| Infinitive | Translation | Full participle | Reduced form |
| glimme | glimmer | glommen | glom |
| klimme | climb | klommen | klom |
| komme | come | kommen | kaam/kôm |
| nimme | take | nommen | naam/nôm |
| swimme | swim | swommen | swom |
| fange | catch | fongen | fong |
| hingje | hang | hongen | hong |
| sjonge | sing | songen | song |
| springe | spring | sprongen | sprong |
The variation seems to be dialectical, the shortened forms being preferred in the east. There is a small intersection with the western area in which -d is added. In this transition zone, a participial form like fongd caught has been attested.
The verbs komme to come and nimme to take may also take a participle with -d, as in komd and nomd. These forms are not restricted to the intersection area. Rather the opposite is the case, as they have also been attested in the north, although the core area of these forms remains in the west.
The addition of -d, and also the reason of better visibility of the participial form, is mentioned in Tamminga (1964:332) and Hoekstra (1992) and in some recent grammars. Miedema (1968) reports that the phenomenon already existed in the first half of the 19th century in the village of Skraerd in the midwest, and Miedema (1986:69) even found traces in a text written in the now extinct dialect of the village of Molkwerum, situated in the deep southwest. In the dialect survey in Van der Veen (1993) various maps of d-addition can be found. The only in depth study is Ybema (2013), which is mainly based on the data of Goeman (2008).
The truncation after /ŋ/ is observed in Tamminga (1984:90). A dialect map of the participles of komme to come and nimme to take may be found in Hof (1933:183). According to Knop (1954:207) the suffix -en must also have disappeared after [ŋ] and [m] on the island of Terschelling.
Especially in the speech of the younger generation we can hear forms of the second person singular past tense with insertion of an element -de- or -te-. Examples are seagdest saw-PRET-sSG saw and holptest help.PRET-PRET-2SG helped. No doubt, the source of the elements should be found in the paradigm of the weak verbs of class I, with its past tense suffixes -de and -te. The distribution is also similar, that is, -te follows a voiceless stem, and -de a voiced one. The net result, the endings -dest, and -test, is similar to what we find in class I of the weak verbs.
Apparently, the change began in those strong verbs that have an identical singular second person form for both the present and past tense. For the voiceless stems, this is quite striking in the pair witst and wist of the verb witte to know, which, although spelled differently, have the same pronunciation. Something comparable, at least in some dialects, applies to the second person forms of the verbs moatte must and doare dare. With respect to voiced stems, the origin can be taken to be in the verbs sizze to say and lizze to lay, with their common present and past tense forms seist and leist. Later on, the suffix -de spread via other stems ending in a vowel:
| Original | New | Translation | Infinitive |
| do wiest | do wiedest | you were | wêze |
| do hiest | do hiedest | you had | hawwe |
| do diest | do diedest | you did | dwaan |
| do stiest | do stiedest | you stood | stean |
| do giest | do giedest | you went | gean |
| do soest | do soedest | you should | sille |
| do koest | do koedest | you could | kinne |
| do woest | do woedest | you wanted | wolle |
The first step in the spread of the suffix -te was seen in stems ending in /xt/:
| Original | New | Translation | Infinitive |
| do brochtst | do brochtest | you brought | bringe |
| do tochtst | do tochtest | you thought | tinke |
| do sochtst | do sochtest | you sought | sykje |
| do kochtst | do kochtest | you bought | keapje |
| do mochtst | do mochtest | you might | meie |
| do fochtst | do fochtest | you fought | fjochtsje |
Data for this section have been drawn from Hoekstra (2013). He gives an analysis of the putative historical development, and also points at an extension of the insertion to certain complementizers, with forms like attest if you, dattest that you and toendest when you.
We have seen irregular weak verbs belonging to class I that some weak verbs have undergone shortening in the second and third person of the present tense, in the past tense and in the past participle. With respect to some strong verbs we see something comparable. Thus the verb bite to bite which has a stem vowel /i/ may have a second person singular present tense bitst and a third person bit, both with a vowel /I/. This is the result of a historical shortening that dates from the Old Frisian period.
Since this shortening did not occur in the past tense and the past participle, it meant that the deviating alternant had a weak place in the paradigm, weaker than the output of shortening of the irregular weak verbs of class I. This had the consequence that these deviating forms have been fully levelled out nowadays, with one dialectical exception. However, in the 19th century and in the Middle Frisian period (1550-1800), we can come across alternate forms in the second and third person of the present tense. As far as the spelling is reliable, we might conclude that the result of shortening is the sound /I/. The input sound is /i(:)/.
The following verbs have been observed in being involved in the change (the shortened forms are given in the spelling of the source):
| Infinitive | Observed 3SG.PRES | Translation |
| bite | bit | bite |
| glide | glit/glidt | glide |
| ite | it | eat |
| krite | krit | cry |
| ride | rit/ridt | ride |
| smite | smit | throw |
(Dijkstra 1900-1911) mentions the forms bit and glidt as still existing in a northeastern region. This is conceivable in as far as in the dialect of the island of Schiermonnikoog the alternation is still alive and well. In addition to the verbs in the table above, it appears that (in the dialect's orthography) also the verbs schyte to shit, slyte to wear and splyte to split are involved.
The source for older Frisian is Hoekstra (1989). He views the change only as a shortening. The forms in the dialect of Schiermonnikoog can be found in Fokkema (1969:44-45). The alternation is reminiscent of what may be observed in Lower Saxon dialects and in German on a larger scale. See Bloemhoff (2008:100-102) for more details.
Irregularity tends to be done away with, especially in less frequent forms. We see this phenomenon at various levels: with respect to deviating forms in the present tense, to the form of the past tense as a whole, and even to the verb itself, which can turn to a regular verb in its entirety.
One field which levelling has taken place rather massively is in the classes which show stem alternation in the present tense. The deviating stems of the second and third person singular are replaced by those of the rest of the paradigm of the present tense. Such levelling has been signalled in the sections on irregular weak verbs of class II, also in the ones of class I, in monosyllabic verbs and in verbs that display lowering.
Levelling in the paradigm of the irregular weak verbs of class II is discussed in Tiersma (1978).
Of the three potentially different stems of strong verbs - present tense, past tense, past participle - the one of the past tense is less frequent in common usage. The effect is that its stem may disappear and become similar to one of the other stems, mainly to the one of the past participle since this is also used to refer to an event that took place in the past. We see this effect most prominently with those verbs in which stem-final /k/ has been palatalized to /ts/. An example is the triple brekke to break - briek - brutsen, which is replaced by brekke - bruts - brutsen, especially in the south. Other verbs following this pattern are mentioned in the section about strong verbs. Another case in which the form of the participle superseded the form of the past tense can be observed is the set of verbs with the rhyme -iuwe, like bliuwe to stay or skriuwe to write. The result for a verb like bliuwe is that the stem bleau of the past tense may have turned to bleaun, similar to the participial form bleaun. For more information about this change, see the table above.
The strength of the past participle has possibly been most intense in the verb ferlieze to lose. In the standard language, this has the triple ferlieze - ferlear - ferlern. Several speakers in the southwest have totally weakened this verb on the basis of the participle, and thus have changed to the triple ferlerne - ferlernde - ferlernd. Two factors may have contributed to this remarkable transition. Firstly, the variation in final consonants /z/ ~ /r/ ~ /n/ (the spelled <r> in the participle is not pronounced because of R-deletion) builds an extra complication for the already existing vocalic variation. Secondly, the participle already received a weak ending -d in the relevant dialects; this phenomenon has been dealt with in developments with respect to the ending of the strong past participle.
The participle is not the only force to replace the form of the past tense. Sometimes, the work can also be done by the infinitive in connection with the present tense. Thus with respect to the verb bliuwe remain, there are also speakers who weaken the past tense. They then replace the original triple bliuwe - bleau - bleaun by bliuwe - bliuwde - bleaun. In the south, the preterite of lêze to read has likewise become weak: lêsde instead of strong lies.
On the other hand, there is also a minor pattern in which the participle must have been weakened, whereas the past tense remained strong. This is reported in the 19th century for the verbs skowe to shift and stowe to dash, to rush. The participle is reported to be weak (skood and stood, respectively), whereas the past tense is strong (skau and stau). Nowadays, these verbs are weak in all of their forms.
The levelling in verbs like brekke and bliuwe is dealt with in Tiersma (1980:82-84). One can get a glimpse of the dialectical spread of the preterite forms stiek and stuts of the verb stekke to stick in Van der Veen et al. (2001:165). The rise and spread of the variants with -uts is also discussed in Loopstra (1937). Piebenga (1935) already notes the stem ferlern for the present tense of ferlieze to l