Many other verbs, however, undergo more significant alterations to transform from references to present-tense actions to those representing actions performed in the past. Such words are called irregular verbs.
The simple past, the tense form that describes what previously occurred, is fairly straightforward once one assimilates the forms for each irregular verb. But complications set in when the past participle—a verb assisted by an auxiliary verb, or a past-tense form of the verb to be—is employed.
Some past-participle forms are easily distinguished from their simple-past counterparts, as in the case of ate/eaten, for example, or saw/seen (“I ate already”/”I had eaten already”; “We saw the movie”/”We had seen the movie”). Others, however, often literally give writers pause. Many of them are presented below in sample sentences with simple-past usage for comparison: