As with other Romance languages, Catalan shows an extensive and varied verb grammar.

The classical description of Catalan verb grammar (due to Pompeu Fabra) recognises three main conjugations, with cantar, perdre and dormir as the type verbs. These derive from the Latin first (-āre), second+third (-ēre and -ere), and fourth (-īre) conjugations respectively.

The description maintained here is based mostly on the division made by Fabra, with further splits based on the ending of the infinitive form, along with some differences in the patterns of the formation of conjugated forms. Varieties in formation based on the stem-final letter(s)/sound(s) are detailed on the pages of each individual conjugation, and any irregularities are noted. However, not all changes are unpredictable, see below.

A substantial number of verbs have some kind of irregularity. This means that some of its forms are created in a way that is unpredictable and goes contrary to the normal rules of conjugation. These verbs are listed at Appendix:Catalan irregular verbs. However, not all changes are unpredictable; some are a consequence of spelling rules and can therefore be predicted and applied regularly. See Appendix:Catalan orthography for an overview, as well as examples of how those rules apply to verbs and other words.

It is possible to construct the conjugated forms of many verbs with knowledge of only four forms. These four forms are called the principal parts of the verb, and they are:

1. The infinitive
2. The first-person singular present indicative
3. The first-person singular imperfect indicative
4. The past participle

Knowing just the first two principal parts will allow you to conjugate regular verbs and a few slightly irregular ones, but knowing all four will allow you to conjugate almost all verbs, even those that are usually considered 'irregular' in traditional grammar. As it turns out, most irregular verbs are actually very regular, they simply have a different set of rules.

Most verbs have only one stem, which can be derived from any of the four principal parts. However, several verbs have two or more stems. Knowing the principal parts allows you to recognise when to apply which rules to form the stems of each conjugated form of a verb.

To form the stem of the present participle and the first- and second-person plural present indicative:

• If principal part 3 ends in -ia (not -ïa) preceded by a vowel:
  • Then if the infinitive ends in -r:
    • Then remove -r from the infinitive.
    • Else remove -ure from the infinitive and add -i.
  • Else remove -ava, -ia or -ïa from principal part 3.

To form the stem of the second and third person singular and the third person plural present indicative:

• If principal part 2 ends in -o:
  • Then remove -o from principal part 2.
  • Else if the infinitive ends in:
    • -ure: Remove -re from the infinitive.
    • -r: Remove -r from the infinitive and add -u.
    • Otherwise: remove the ending -dre, -re, -er, -ir from the infinitive.

To form the stem of the imperfect indicative:

• Remove -ava, -ia or -ïa from principal part 3.

To form the stem of the preterite, first- and second-person plural present subjunctive and imperfect subjunctive:

• If principal part 2 ends in -o:
  • Then use the present participle stem.
  • Else take principal part 2 and replace -c with -gu-, and -sc with -squ-.

To form the stem of the first, second and third person singular and the third-person plural present subjunctive:

• If principal part 2 ends in -o:
  • Then remove -o from principal part 2.
  • Else take principal part 2 and replace -c with -gu-, and -sc with -squ-.

To form the stem of the future and conditional:

• If the infinitive ends in -e:
  • Then remove -e from the infinitive.
  • Else take the infinitive.

This group contains verbs all verbs in ending -ar. These verbs characteristically form the imperfect tense with infix -av- rather than -i- as in the other two conjugations.

The majority of Catalan verbs belongs to this group, and almost all of them are completely regular and inflected the same way. There are no subgroups, so for all but a handful of first conjugation verbs, the infinitive is the only principal part that is needed to determine all forms.

Model verb: cantar

This group contains verbs in -re and -er. Apart from a few verbs, the verbs of this conjugation class have stress on the stem rather than on the infinitive ending. This conjugation is by far the most irregular, and many verbs have unusual changes in the stem.

There are several subgroups within the second conjugation. They are split up based on the final consonants of the stem. Historically speaking, the infinitive ending of these verbs was unstressed -ere, in which the first vowel usually disappeared and the ending contracted into -re. However, in some verbs the final consonant couldn't easily be combined with this ending. For example, the stems tem- or torç- did not "fit" with the ending -re: temre and torçre were hard to pronounce in the earlier history of Catalan. Thus, in these verbs the first vowel remained, and the second was dropped instead, resulting in unstressed -er. In modern Catalan, stems ending in the following consonants will have unstressed -er in the infinitive: -m, -ny, -rr, -x, -c/-ç, -s. The future and conditional forms are based on the infinitive, so the verbs which have kept the first -e- in the infinitive will also have it in the future and conditional (teme-ré, but perd-ré).

There are some verbs with a stressed ending -er in the infinitive. These are leftovers from the Latin second conjugation (stressed -ēre) which almost completely merged into the third conjugation (unstressed -ere) in Catalan. They do not form a coherent group, however, and many of them have alternative infinitives in -re. They are therefore best considered as irregular infinitives belonging to one of the other groups, and not as a group by themselves.

It is hard to say exactly what is "regular" when considering the second conjugation. However, the most verbs of this group are almost the same as the third conjugation verbs without the -eix- infix. The verbs of this type are those whose final consonant cannot be easily combined with the velar infix (see below). More specifically, this type contains the second conjugation verbs whose stem does not end in -l, -n or a vowel. The verb cerndre also belongs here.

As noted above, the forms of the infinitive, future and conditional depend on the final consonant. Both varieties are shown here.

Model verb: perdre

Model verb: témer

Characteristic of the second conjugation is the appearance of many verbs which have an additional -g- attached to the end of the stem in some of the forms. This is called the "velar infix". This infix usually appears in the forms of the preterite and subjunctive (both present and imperfect). It also appears in the first-person singular present, where it becomes -c due to final devoicing; these forms do not have the -o that the regular verbs do. In addition, many verbs have a velar infix in the past participle.

The expansion of the velar infix /g/ in this verbal subclass, while its formation is debated, might be the result of the morphologic reinterpretation from the final consonant of some very frequent verbs with a velar in the present theme like DICO > dic (I say) and the consonantization of the aspectual mark of verbs with a strong perfect in -UI- like DEBUIT > dec >> degué (ought)^[1]

Second conjugation verbs with stems ending in -l or -n generally have a velar infix in all of the above forms (but note cerndre which does not have it). In these verbs, an additional -d- is inserted into the infinitive, but this is not part of the stem and it is removed in most forms (but not in the future and conditional, since those are based on the infinitive).

Model verb: prendre

Second conjugation verbs with stems ending in a vowel will have an infinitive ending in -ure. A few verbs (dur, dir, fer) have just -r. Vowel stem verbs normally use the velar infix as well.

This group of verbs can be further subdivided based on how the final -u of the stem behaves. This is particularly noticeable in the forms of the imperfect tense:

1. The stem-final -u disappears between vowels, creating a hiatus. The imperfect ending is -ïa /ˈiə/, with a diaeresis on the i to separate it from the preceding vowel.
2. The stem-final -u becomes a consonant -v- between vowels (just like in the adjective blau, feminine blava). The imperfect ending is -via /ˈβiə/.
3. The stem-final -u becomes consonantal -i- /j/ between vowels, and the stem is stressed instead of the ending. The imperfect ending is -ia /jə/. Verbs of this type tend to have the vowel -e- in the imperfect tense stem, even when the other forms have another vowel.

Model verb: complaure

Model verb: beure

Model verb: creure

This group contains all verbs ending in -ir, except for tenir, venir and dir and their derivatives. It is a fairly large class with many regular verbs.

The verbs in this group add an infix -eix- between the stem and the ending, whenever the ending does not carry stress. Most third conjugation verbs follow this conjugation, and most of the verbs are regular.

These verbs are often referred to as "inchoative" verbs, because the -eix- infix descends from the Latin suffix -ēscō which was used to form inchoative verbs. This name is a misnomer, though, as these verbs are not necessarily inchoative in meaning in modern Catalan.

Model verb: servir

The verbs in this group do not add the infix -eix-, and are sometimes referred to as "pure" third conjugation verbs. Only around 10% of the third conjugation verbs follow this pattern, and there is a tendency for even those verbs to be conjugated like the larger and more productive -eix- class instead. As a consequence, this group consists mostly of old "relic" verbs that tend to be used relatively frequently.

Model verb: dormir

These verbs can be conjugated either with or without -eix-. Sometimes there is a difference in meaning, but usually the forms without -eix- are just more archaic.

• arrupir-se
• brumir
• consumir
• lluir
• mentir
• resumir