If a verb belongs to third conjugation what will the second principal part end in?

If a verb belongs to the third conjugation, its second principal part (the perfect stem) will end in -i.

Here are some examples:

* Regere (to rule) -> rexi (I ruled)

* Agere (to do) -> egi (I did)

* Capere (to take) -> cepi (I took)

The third conjugation is characterized by the ending -ere in the present infinitive and -i in the perfect stem.