Modal verbs do not exactly translate into their English equivalents. Each modal verb has several meanings that have several unique meanings. Because modals are used commonly, they forms and meanings must be memorized. In other words, the I, he, she, it, and you singular forms have different stems from the we, you plural, and they plural forms . Both the present and past perfect forms follow a the same pattern of a helper verb in the second position and the modal verb or verb phrase on the end.
All modal verbs use the same helping verb, haben .
What the ending of a present or past perfect sentence depends on whether there are two or three verbs involved. The present and past perfect forms of modal verbs with dependent verbs are actually easier that without the dependent infinitives. When the modal verb is moved from the second position to the end of the sentence, the dependent infinitive stays an infinitive and the modal takes the end position. The resulting formation called a double infinitive . The word order of dependent clauses is switched.