Many verbs take “-ed” in the past tense, for example: jump – jumped; play – played. However, there are also very many verbs that are irregular, that is, the spelling of the word changes in the past tense. There are no rules to follow for the spelling of irregular verbs. Examples:

Present tense: I am happy. Past tense: I was happy.

Present tense: I have a headache. Past tense: I had a headache.

Present tense: I choose the strawberry ice-cream. Past tense: I chose the vanilla ice-cream.

Present tense: I think about you every day. Past tense: I thought about you every day.

There are many examples of irregular verbs in English – and because there are no rules, you just have to learn them.