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.

By language

English

In English, the verb love derives all its forms systematically (love, loves, loved, loving), and since these can all be deduced from the basic form (the citation, dictionary, or lexicographic form, which in English is the bare infinitive), no other principal parts have to be learned. With irregular verbs like the verb sing, on the other hand, the forms sang and sung cannot be deduced, so the learner of English must memorise three principal parts, sing – sang – sung. From these, all other forms (like sings or singing) can be deduced. (See also English verbs, English irregular verbs, English as an additional language.)

Latin

In Latin, most verbs have four principal parts. The verb for "to carry" has the parts portō – portāre – portāvī – portātus. Portō is the first person singular form of the present ("I carry"), but the infinitive portāre ("to carry") is also needed to deduce all the forms of the present stem. The perfect stem portāvī ("I carried") and the supine stem portātus (required for the perfect passive participle). Another example, the verb "to praise" has the parts laudā - laudāre - laudāvī - laudātus. Laudā and laudāre, the present active indicative first person singular and the present active infinitive are needed to deduce the present stem. Laudāvī is needed for the perfect stem, while laudātus is required for the perfect passive participle.

Spanish

In Spanish, verbs are traditionally held to have only one principal part, the infinitive, by which one can classify the verb into one of three conjugation paradigms (according to the ending of the infinitive, which may be -ar, -er or -ir). However, some scholars believe that the conjugation could be regularized by adding another principal part to vowel-alternating verbs, which shows the alternation. For example, herir "to hurt" is usually considered irregular because its conjugation contains forms like hiero "I hurt", hieres "you hurt", where the vowel in the root changes into a diphthong. However, by including the first person singular, present tense, indicative mood form (hiero) as a principal part, and noting that the diphthong appears only when that syllable is stressed, the conjugation of herir becomes completely predictable. (See also Spanish verbs, Spanish conjugation.)

Scottish Gaelic

In Scottish Gaelic there are two principal parts for the regular verb: pog – pogadh. All finite forms can be deduced from the imperative pog ('kiss!'), all non-finite forms from the verbal noun pogadh ('kissing'). The ten irregular verbs can, with only two or three small aberrations (unexpected lenition), be deduced from four principal parts.

See also

• Regular verb
• Irregular verb
• Grammatical conjugation
• List of Latin verbs including all four principal parts
• Root (linguistics)
• Lemma (linguistics)