Rules for writers, Tenth edition - Diana Hacker, Nancy Sommers 2021

Do not omit -ed endings on verbs
Choose appropriate verb forms, tenses, and moods
Grammar

The verb ending -ed is sometimes not fully pronounced with words and phrases such as asked, fixed, pronounced, supposed to, and used to. While the meaning of such words is often clear while speaking, include -ed endings in academic writing to avoid confusion.

Past tense

Use the ending -ed or -d to express the past tense of regular verbs. The past tense is used when the action occurred entirely in the past.

Past participles

Past participles are used in three ways: (1) following have, has, or had to form one of the perfect tenses; (2) following be, am, is, are, was, were, being, or been to form the passive voice; and (3) as adjectives modifying nouns or pronouns. The perfect tenses are listed in 27f, and the passive voice is discussed in 8a. For a discussion of participles as adjectives, see 49b.