Before, After (前に・あとで)

前に always takes the dictionary form even in a past-tense sentence, 食べる前に行きました, “I went before eating,” never 食べた前に. あとで works the opposite way, always the past た-form, even when the whole sentence describes a habit or the future, 食べた後で寝ます.

Attached to a noun instead of a verb, both just need の between them, 授業の前に, パーティーの後で, “before class,” “after the party,” a much simpler pattern than the verb forms above.