Conversion is a directional process, linking an input and an output form that are formally but not semantically identical Don (1993), Booij (2002: 134-136), Bauer (2013: 545), that is, conversion is comparable to derivation, but there is no affix, at least not a visible one. For this reason, many researchers see it as a special case of derivation; the term zero-affixation is used as a synonym for conversion (e.g. in Marchand (1969: 359 ff), cf. also Smessaert (2013: Ch. 6)).

There are various types of conversion in Dutch; conversion into verb is the most frequent and the most productive. Below is an overview, sorted according to output category:

• Output category verb. As Booij points out, all verbs that are the result of conversion have regular (weak) inflection.
  • Conversion into verbs, or "verbification", is productive in Dutch ("you can verb almost any noun"), at least for simplex nouns. Booij (2002:135) describes the general semantics of N-to-V conversion as 'to V, with N playing a role in the action denoted by V'. He writes "Due to the very general meaning contribution of the conversion construction, the range of specific meanings of conversion verbs is enormous." The meaning classes he distinguishes are illustrated in the table below:
    Table 1

    Meaning	Base Noun	Resulting Verb
    to behave as N	ijsbeer polar bear	ijsbeer pace up and down
    	moeder mother	moeder mother
    	tuinier gardener	tuinier garden
    make into N	bundel bundle	bundel bundle
    	knecht servant	knecht to subjugate
    to do something with N	huis house	huis live
    	schroef screw	schroef screw
    	computer computer	computer work with a computer
    	zon sun	zon sunbathe
    to produce N	big piglet	big pig
    	bloesem blossem	bloesem blossem
    	jong young one	jong give birth

    Most of the converted nouns are simplex ones, or compound nouns with a simplex head such as voetbal football, to play football. It is not easy to find derivationally complex nouns that feed conversion; a case in point is tuinieren to garden from the derived noun tuin.ier gardener.

    In Dutch and many other European languages, children use this kind of conversion productively from a young age Clark (1993: Ch. 11).

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    According to Booij, "The semantic versatility of this word-formation process [...] is certainly an important cause of its high productivity." On the other hand, semantic versatility could also work against productivity, as the meaning of the verb can be too underspecified to be useful.

  • Conversion from adjectives is not productive, but there are quite a few verbs that are the result of conversion of adjectives. Again, various meaning classes can be distinguished:
    Table 2

    Meaning	Base Adjective	Resulting Verb
    to make A	wit white	wit whiten
    	zuiver pure	zuiver purify
    	openbaar public	openbaar reveal
    to become A	rot rotten	rot rot
    	bruin brown	bruin tan
    to behave in an A manner	snel fast	snel hurry
    	suf drowsy	suf doze

    This process is not productive: one cannot take just any adjective like groot big, large and turn it into a verb - possibly because the process is blocked in this case by the much more productive proces of ver- prefixation: vergroot to enlarge is fine. Some verbs converted out of adjectives have more than one meaning, e.g. the verb from the adjective krom bended, crooked can mean 'to become bended', 'to make bended' and (with a reflexive pronoun) 'to bend onself, to incurve'.
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    There are a few verbs that result from conversion of bases from other categories: pronominal bases are found in jijen en jouen be on (over-)familiar terms (< jij you.NOM, jou you.OBL, a conjunction in maren to keep raising objections (< maar but), and interjections in bonjouren to say goodby, to throw out (< Fr. bonjour farewell), sakkeren to swear (ultimately from French sacre Dieuholy Lord or something like that) (Smessaert (2013: 85)). Smessaert claims that jammeren to wail also derives from an interjection (jammer alas), but it is also possible that both the verb and the interjection are conversions of the noun jammer sadness (that is used as an adjective as well, cf. Etymologiebank).

• Output category noun
  • A few native adjectives can be used as nouns, the meaning is usually 'something that has the property A', gender is neuter: het nat the wet can be used to refer to anything that is wet, from beer to the sea; cf. also in het wit in the white (dressed) in white, in het lang in the long in a long dress, het geheel the whole, in het openbaar in the public publicly, in het geheim in the secret secretly, een naakt a nude, het origineel the original. As the examples show, adjectives functioning as nouns are of neuter gender, selecting the article het.

    Many non-native adjectives can also be used as nouns of common gender, denoting personal names, e.g. crimineel criminal, liberaal liberal, virtuoos virtuoso (Smessaert (2013: 82)).

  • Three classes of verbs can be converted into nouns:
    • simplex verbs: haat hate > de haat the hatred, stroom stream > de stroom the stream; the electricity, loop walk > de loop the walk, the course, huiver shiver > een huiver a shudder. Input verbs are usually monomorphemic, monosyllablic, native; output nouns are of common gender, and usually denote the process or the result.
    • prefixed verbs: ontbijt ont-bijt, start to bite have breakfast > het onbijt breakfeast, verblijf ver-blijf stay > het verblijf the stay. Output nouns are usually of neuter gender, with a few exceptions like de verbouw the cultivation, the rebuilding < verbouw cultivate, rebuild and de herbouw the process of rebuilding < herbouw re-build rebuild.
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      Conversion is not the only way to turn verbs into nouns. From the prefixed verb verhuis ver-huis move (house) both the conversion form verhuis and the suffixed form verhuizing exist; the former, however, is rarely found outside the South of the language area (Brabant and Belgium). Meaning specialisation occurs as well in the case of doublets: whereas beschrijving description is the unmarked nominalization for the verb beschrijf describe, the conversion form beschrijf is a technical term in the Belgian real estate world.

    • particle verbs: aan.bouw on-build to build, to attach > de aanbouw the process of build, the annex, uit.groei out-grow to grow out > de uitgroei the grow, the outgrowth. Output nouns are of common gender.
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    As haat and comparable monomorphemic cases are systematically of common gender, just like the particle verbs like aanbouw, whereas the conversions of prefixed verbs such as ontbijt are almost exceptionless of neuter gender, we have to assume (at least) two different subtypes of V-N conversion.

  • All infinitives can function as nouns, gender is always neuter (het zingen the singing, het geven the giving, het slaan the hitting). The argument structure of the verb is often preserved, where arguments are either expressed as lefthand parts of compounds or as proposition arguments: het pianospelen the piano.play the pianoplaying, het roken van sigaren door hooglararen the smoking of cigars by professors, het wandelen daarheen the walking in that direction.
  • Participles do not convert into nouns, as they take a suffix -e if they function as nouns (just like ordinary adjectives): het gedane what has been done, het zijnde what is.
  • A few prepositions have been converted into nouns, e.g. de voors en tegens van deze aanpak the pros and cons of this approach; new cases are unlikely.
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    Trivially, almost any piece of language can be used as a (neuter) noun when used metalinguistically: het "van" van mijn buurman bevat een andere "a" dan mijn "ga zitten" the "van" of my neighbour contains a different "a" than my "ga zitten" my neighbour's "van" has a different "a" than my "ga zitten".

• Output category adjective is extremely rare.
  • Only a few nouns have turned into adjectives: there are some (foreign) names of materials that can also be used as noun premodifiers (but do not show adjectival inflection): een aluminium fiets an aluminium bike, een jute zak a burlap sack, een mohair trui a mohair sweater. Another group consists of names of members of religious orders such as kartuizer Carthusian that can be used both as a noun and as and adjective (Smessaert 2013: Ch. 6).
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    Constructions like English New York State of Mind (a 1976 song by Billy Joel) are impossible in Dutch. Of course, it is not impossible to express this kind of meaning in Dutch, e.g. by turning the noun into an adjective by means of suffixation (het echte Amsterdamse gevoel the real Amsterdam feeling), or by means of compounding (het echte Amsterdamgevoel the real Amsterdam feeling).

  • Verbal stems cannot be used adjectivally.
  • Past participles of transitive and ergative verbs freely function as adjectives, both attributively and predicatively: een gevallen vrouw a fallen woman, een vrouw, eenmaal gevallen a woman, once fallen. Regular ("weak") participles show adjectival inflection een verkocht schilderij a sold painiting, de verkocht.e bruid the sold bride. Verbal arguments may carry over: de door moeder stijf geklopte room the through mother stiff whipped cream the cream that was whipped by mother. Participles of intransitive verbs cannot function as adjectives: *de geademde lucht the breathed air. Present participles of most verbs can be used as adjectives as well, mainly attributively: een vallend.e ster a falling star (showing inflection), het hijgend(e) hert the panting deer (?de ster is vallend the star is falling, ?het hert is hijgend the deer is panting are very strange). Various present participles, however, have lexicalised into "normal" adjectives: het bevel klonk dringend the command sounded urgent (< dring to push, to press).
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    The present participle lopend walking can occur in a special construction with a form of the verb of be zijn or verbs of locomotion such as komen come and gaan go where it functions as a manner adverb: Ik ben lopend I am walking I am here by foot, we zijn lopend gekomen we have walking come we came by foot (in various dialects one finds the variant lopens /lo-pəs/). Other verbs seem impossible here.

    Smessaert (2013: 84) observes that meaning specialization can go hand in hand with change of the stress pattern, another sign of lexicalization, e.g. aan'houdend continuous (< 'aanhouden to persist, to arrest), opvliegend quick-tempered (< 'opvliegen to fly up).

• Some prepositions (mostly used in more formal registers) originate as participles: gedurende during (cf. English during, German während, French durant), overwegend(e) considering, hangende pending, gegeven given.
• At least four verbal stems have developed uses as discourse particles: hoor hear, kom come, kijk look, zeg say(Kirsner 1990, De Vriendt 1995, Van Olmen 2013).
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  It is unclear whether these particles are the result of conversion: it may also be the case that they have a clausal origin. This analysis seems particularly appropriate for (sentence-final) hoor that might be derived from a tag question hoor je? hear you do you hear me? do you understand?. For dialects, other particles with a verbal origin have been described, e.g. denk think I presume; in Afrikaans, glo (ultimately from Dutch geloof believe) has developed into a full-fledged modal particle possibly, I think.