In case the pronoun do 2SG follows the verb in a tensed clause, it cannot be independently present. Instead, it must cliticise onto the verb:

The grammatical example could be the result of assimilation of the voiced /d/ of the full form do you to the voiceless ending of the verb. However, that does not explain why the presence of the full form, which could otherwise occur in slow or emphatic speech, is forbidden even in slow or emphatic speech. Furthermore, pronouns can ordinarily be premodified by certain adverbial elements like sels even. An example is given below:

This is excluded in the case of the 2SG subject pronoun:

The same pattern of facts is found in case the pronoun follows the complementiser:

These facts may be related to the fact that the 2SG agreement ending -st 2SG is the only ending that must appear on the complementiser (if present) and on the tensed verb. Hence an embedded clause has an agreement ending both on the complementiser and on the verb, as shown in the example below:

In case the pronoun precedes the verb in a main clause, the pronoun may be absent altogether. This phenomenon is also referred to as pro-drop:

In case the pronoun follows the verb or the complementiser, the pronoun may also remain absent:

Alternatively, the pronoun may be cliticised onto the verb or complementiser. The pronoun may retain its full vowel or it may be weakened to a schwa:

Weakening to schwa was common in older Frisian, but it sounds old-fashioned nowadays. Nowadays, either the full vowel is retained or the pronoun is altogether absent. In case the pronoun is embedded in a coordination structure, it cannot be completely absent. Instead, it must cliticise onto the complementiser: