Principal parts

The principal parts (/prɪnsɪpəl pɑ:ts/) of a verb are those four forms from which all other forms may be constructed. For example, the principal parts of eat are eat, ate, eaten, eating. Some verbs are defective verbs and do not have all of these forms available for use. For regular verbs these are regular (albeit sometimes with minor spelling changes), but irregular lexical verbs are, well, irregular.

Names	Examples	Notes
Base form first form	eat, play	Used, without change, as the bare infinitive, first and second persons singular of the Present Simple inflected tense. With the addition of third person -s with certain other changes with some verbs (see Present Simple: Form), it is used for the third person singular for of that tense.
Preterite, second form marked form	ate, played	Used for the past simple tense. For regular verbs it is identical to the past participle.
Past participle third form	eaten, played	Used for the perfect aspect and the passive voice. For regular verbs it is identical to the preterite.
-ing form, present participle Fourth form	eating, playing	Used for the progressive aspect.