From Wikipedia on principal parts:

In language learning, the principal parts of a verb are those forms that a student must memorize in order to be able to conjugate the verb through all its forms. […] The principal parts of an English verb are the infinitive, preterite and past participle.

In English, the present participle is used for verb conjugation (e.g. present continuous). Why is it not considered a principal part?


The present participle can be systematically deduced from a principle part, namely the infinitive. In pronunciation, you just append ing. In writing, it is a little bit more complicated due to the peculiarities of English orthography, but it’s still systematic. For example, you have be → being, go → going, make → making, say → saying, occur → occurring.

Therefore, once a student knows the infinitive, they can also form the present participle. There is no need for them to memorise it separately for each verb. This however is the defining nature of principal parts. Hence, the present participle is no principal part.

By contrast it is not possible to derive the simple past from the infinitive. There is no rule that captures take → took, go → went, make → made, and like → liked. Hence, students need to memorise the simple past for each verb (or at least the many verbs whose simple past is not simply formed by adding ed to the infinitive). Hence the simple past is a principal part.

  • That's right: there are no irregular -ing forms. – tchrist Jan 15 '17 at 14:18
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    Some exceptions include forms such as singeing, dyeing, ageing, rueing, cacheing and whingeing, where the e may be retained to avoid confusion with otherwise identical words (e.g. singing), to clarify pronunciation (for example to show that a word has a soft g or ch), or for aesthetic reasons. – tuxestan Jan 15 '17 at 15:11

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