Went, bought, taken

The rule, as people use it

Most verbs make the past with -ed: walk, walked; call, called. Irregular verbs don't. They have their own past form and often a third form for "have" and passive sentences: go, went, gone; take, took, taken; write, wrote, written. There are around two hundred of them, but you don't need them all. About forty cover almost everything you'll say in a day, and they're the most common verbs in the language: be, have, do, say, get, make, go, know, take, see, come, think, give, find, tell, feel, leave, buy, bring, forget.

They fall into rough families, which helps your memory. Some don't change at all: cut, put, let, hit, cost. Some share the same past and third form: buy, bought, bought; bring, brought, brought; think, thought, thought. Some change the middle vowel: sing, sang, sung; drink, drank, drunk; begin, began, begun.

The two mistakes you'll hear most are adding -ed anyway ("I buyed", "she goed") and using the second form after "have" ("I've took it", "she's went home"). After have, has or had, reach for the third form: "I've taken it", "she's gone home".