When do you use 'avoir' or 'être' for the passé composé?

The passé composé is composed of two parts - the auxiliary verb (avoir or être) in the present tense and the past participle of the verb you want to put into the past tense (for example, jouer> joué). The majority of verbs take avoir in the passé composé, however verbs that take être often express motion or change of place, state or condition, for example aller (to go), sortir (to go out), devenir (to become). However rester also takes être in the passé composé so does not follow this rule! As is often the case in French, you just have to learn the verbs and a classic way to do this is with the acronym DR & MRS VANDERTRAMPP: each letter represents a verb that takes être Devenir, Rentrer, Monter, Retourner, Venir, Arriver, Naitre, Descendre, Entrer, Revenir, Tomber, Rester, Aller, Mourrir, Partir, PasserAlso, don't forget that with être verbs the past participle needs to agree with the subject (you, if you're speaking in first person). For example, if you're a girl, you add an 'e': Je suis allée au parc, je suis partie de la maison. Or if you're talking about a group of people, you add an 's': ils sont allés au parc, ils sont partis de la maison.