1. The Present Infinitives
Active and Passive

2. Present Passive Infinitive
In English to be is the indicator of the present passive infinitive, just as to indicates the active infinitive.
vocāre = to call vocārī = to be called
In Latin the present passive infinitive is formed in all conjugations except the third by the final –e of the present active infinitive to –i.
In the third conjugation the short –e of the stem is changed to long –i.

3. The Infinitives in all Conjugations
Active Infinitive
Passive Infinitives
(1st) vocāre, to call
(2nd) monēre, to warn
(3rd) regere, to rule
(3rd io) capere, to seize
(4th) audīre, to hear
(1st) vocārī, to be called
(2nd) monērī, to be warned
(3rd) regī, to be ruled
(3rd io) capī, to be seized
(4th) audīrī, to be heard

4. Verte Anglice!
Necesse erat rēgem inīquum ex urbe expellī.