For all regular verbs, the past-tense and past-participle forms are the same (ending in -ed or -d), so there is no danger of confusion. This is not true, however, for irregular verbs, such as the following.

The past-tense form always occurs alone, without a helping verb. It expresses action that occurred entirely in the past: I rode to work yesterday. I walked to work last Tuesday. The past participle is used with a helping verb. It forms the perfect tenses with has, have, or had; it forms the passive voice with be, am, is, are, was, were, being, or been. (See 46c for a complete list of helping verbs and 27f for a survey of tenses.)

The list of common irregular verbs beginning on the next page will help you distinguish between the past tense and the past participle. Choose the past-participle form if the verb in your sentence requires a helping verb; choose the past-tense form if the verb does not require a helping verb. (See verb tenses in 27f.)

The past-tense saw is required because there is no helping verb.

Because of the helping verbs was and had, the past-participle forms are required: was stolen, had fallen.

When in doubt about the Standard English forms of irregular verbs, consult the following list or look up the base form of the verb in the dictionary, which also lists any irregular forms. (If no additional forms are listed in the dictionary, the verb is regular, not irregular.)

Common irregular verbs