The Present Infinitive Passive
You have known the second principal part of a verb as the infinitive for quite a while now. What you have not been told is that it is the present infinitive active. What this means, of course, is that there are other infinitives … other tenses, other voices. You will read about the other infinitive tenses in Chapter 17. For the moment, let's focus on voice.
English has passive infinitives as well; for example, “to break”/“to be broken,” “to love”/“to be loved,” “to write”/“to be written.” Once again, English uses a past participle with a form of the verb “to be.” Latin, on the other hand, has special endings for passive present infinitives.
|First||amā re (to love)||amā rī (to be loved)|
|Second||monē re (to warn)||monē rī(to be warned)|
|Third||mittere (to send)||mittī (to be sent)|
|Third –iō||iacere (to throw)||iacī(to be thrown)|
|Fourth||sentī re (to perceive)||sentī rī(to be perceived)|
The basic pattern for changing active infinitives to passive voice is to change the short e at the end of the active ending to a long ī. The exception to this rule is for third conjugation verbs. For them, since the active infinitive is two short e's (separated by an r), the entire ending is changed to a long ī. This is also one of the few instances when third conjugation –iī verbs behave like regular third conjugation verbs.
Because the present infinitive passive ending for third conjugation verbs is a long ī , it can be very easily confused with the first person singular perfect indicative active. For example, capī