Spanish irregular verbs

Spanish verbs are a complex area of Spanish grammar, with many combinations of tenses, aspects and moods (up to fifty conjugated forms per verb). Although conjugation rules are relatively straightforward, a large number of verbs are irregular. Among these, some fall into more-or-less defined deviant patterns, whereas others are uniquely irregular. This article summarizes the common irregular patterns.

As in all Romance languages, many irregularities in Spanish verbs can be retraced to Latin grammar.

Due to the rules of Spanish orthography, some predictable changes are needed to keep the same consonant sound before a/o and e/i, but these are not usually considered irregularities. The following examples use the first person plural of the present subjunctive:

Other predictable changes involve stress marks, i/y alternances and i-dropping, some of which are sometimes considered as irregularities. The examples are several forms of otherwise regular preterites:

There are two kinds of changes that can affect stem vowels of some Spanish verbs: diphthongization and vowel raising. Both changes affect -e- or -o- in the last (or only) syllable of a verb stem. Diphthongization changes -e- to -ie-, and -o- to -ue-. Vowel raising changes the mid vowels -e- and -o- to the corresponding high vowels: -i- and -u- respectively. Some verbs, in their various forms, can exhibit both kinds of changes (e.g. , , ; , , ).

Some verbs with -e- or -o- in their stem are inherently diphthongizing, whereas others are not: their identities must be learned individually. In a diphthongizing verb, the change turns -e- into -ie- and -o- into -ue- when the syllable in question is stressed, which in effect happens only in the singular persons and third-person plural of the present indicative and present subjunctive, and in the imperative (all other tenses and forms are stressed on their endings, not their stems). Note that the dictionary form always has the vowel, not the diphthong, because, in the infinitive form, the stress is on the ending, not the stem. Exceptionally, the -u- of jugar and the -i- of adquirir also are subject to diphthongization (juega, etc.; adquiere, etc.).

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