What is the difference between the passé composé and the imperfect tense? How do I know which to use?

This is a common question for the native English speaker learning French as it is a concept that isn't so widely used in the English language. The passé composé (perfect) and the imperfect both have specific conditions under which they should be used, and therefore it is important to pay close attention to the context of the sentence you are writing in order to correctly translate the past tense. The passé composé is used to talk about completed actions in the past, often one off events. For example, ‘elle est arrivé hier soir’ (she arrived yesterday evening) talks about a one off event that is completely finished and so the perfect tense is used. Here, ‘hier soir’ is also an indicator that the passé composé should be used as it provides us with a time frame. Be sure to look out for words like this as they can help you understand which tense to use. The imperfect tense has more specific conditions for usage however it is generally used to talk about repeated or habitual actions in the past. For example, if you were to construct a sentence talking about your childhood hobbies, the imperfect would be used; This corresponds to the English ‘would’ in the sense of ‘used to’. The imperfect is also used when giving background information and descriptions, as well as to refer to ongoing past events that have no reference to a time of starting or finishing. The passé composé and the imperfect can coexist in a sentence, and therefore it is vital to study closely the context in which the verb is used in order to correctly translate and interpret the past tense in French.