What are the rules for forming the passe compose/perfect tense using avoir and etre?

Past participles generally follow a simple rule.For verbs ending in -er, the past participle is made by adding the suffix -é to the root:parler (to speak) - parlé dessiner (to draw) - dessiné tomber (to fall) - tombéFor verbs ending in -ir, the past participle is made by adding the suffix -ito the root:choisir (to choose) - choisi finir (to finish) - fini pâlir (to become pale) - pâliFor verbs ending in -re, the past participle is made by adding the suffix -uto the root:descendre (to go down) - descendurendre (to return) - rendu fendre (to split) - fenduThere are, of course, exceptions to this. Here are a few of the most common irregular past participles:devoir (to have to) - dûavoir (to have) - eupouvoir (to be able to) - pufaire (to do/make) - faitsavoir (to know) - suconnaître (to know) - connu voir (to see) - vuboire (to drink) - buvouloir (to want) - voulu