principal parts

Main verbs have four principal parts: (1) infinitive (to decide), (2) past tense (decided), (3) past participle (decided), and (4) present participle (deciding). A regular verb forms its past tense and past participle the same way, usually by adding ‑ed. An irregular verb, however, uses different methods to form its past tense and past participle. Typically, irregular verbs change an internal vowel (I drink, I drank, I have drunk), or they add -en to form the past participle (I choose, I chose, I have chosen).