Italian has a dozen verbs with an irregular infinitive that ends in -arre, a contraction of the original infinitive ending -aggere. Many conjugations for these verbs are based on that original infinitive.
Italian has about 20 verbs with an irregular infinitive that ends in -orre, a contraction of the original infinitive ending -onere. Many conjugations for these verbs are based on that original infinitive.
Italian has a few verbs with an irregular infinitive that ends in -urre, a contraction of the original infinitive ending -ucere. Many conjugations for these verbs are based on that original infinitive.
Auxiliary verbs are also known as helping verbs, because they help form compound conjugations. The key thing to remember about Italian compound conjugations is that it’s the auxiliary verb which conjugates for the required tense or mood; the main verb is always a past participle.
Avere is one of the most common and useful Italian verbs and has irregular conjugations in just about every tense and mood. Avere literally means “to have,” but also serves an an auxiliary verb and is found in many idiomatic expressions.
Dovere is a very common Italian verb with irregular conjugations and an unusual relationship to some of its English equivalents. It has several meanings related to obligation, supposition, and expectation.