Rules. 1 in affirmative sentences, we use was or 2 in negative sentences, we use or weren't. 3 in yes / no questions, we use / were + pronoun + the verb in the base form. 4 in short answers, we use yes / no + pronoun + / wasn't or were / weren't.

In affirmative sentences, we use was or were_.
2 In negative sentences, we use wasn't_ or weren't.
3 In yes / no questions, we use was_ / were + pronoun + the verb in the base form.
4 In short answers, we use yes / no + pronoun + was/ wasn't or were / weren't.