Arabic verb forms (أوزان awzan in Arabic) are numbered from one to fifteen, though only the first ten are in common use. Verbs in each form conjugate similarly, and sometimes a verb’s form indicates some aspect of its meaning.
Within each form some verbs conjugate slightly differently. Each form contains multiple conjugation models, each of which consists of verbs that have exactly the same conjugation pattern. For example, in form I the verb كَسَرَ ‘to break’ has present form أَكْسِرُ ‘I break’, but the verb أَكَلَ 'to eat’ has present form آكُلُ ‘I eat’, so these verbs are in different models even though they are both in the same form.
Most Arabic verbs have roots consisting of three consonants, but occasionally verbs roots may contain four consonants (also known as "quadriliteral roots"). These verbs may appear in one of four slightly different forms, numbered Iq, IIq, IIIq, and IVq. There are also a couple of irregular verbs that do not fit into any verb form.
Form I is the most basic form and does not affect the basic meaning of the verb.
Verbs in form II can be recognized by the shaddah (doubled letter) on their medial root letter. They are often causative or intensive counterparts of verbs in form I. For example, دَخَلَ 'to enter’ (form I), دَخَّلَ 'to bring in’ (form II), كَسَرَ 'to break’ (form I), كَسَّرَ 'to shatter’ (form II).
Verbs in form III have an alif (long ‘a’ sound) after their first root letter. They often have a meaning relating to acting on or with another entity; for example, كَاتَبَ 'to correspond with’, ضَايَقَ 'to bother’.
These verbs can be recognized by their initial أ in the past-tense conjugation, and they are often causative counterparts of verbs in form I. For example, شَعَرَ 'to know’ (form I), أَشْعَرَ 'to inform’ (form IV), صَلُحَ 'to be good’ (form I), أَصْلَحَ 'to correct’ (form IV).
This verb form is created by prefixing تَـ to form II, and it tends to have a passive or reflexive meaning. For example, تَعَلَّمَ 'to learn’, تَزَوَّجَ 'to get married’.
This verb form is created by prefixing تَـ to form III, and it tends to have a reflexive or reciprocal meaning. For example, تَسَارَعَ 'to rush’, تَكَاتَبَ 'to correspond with each other’.
This verb form is created by prefixing نـ or اِنـ to form I and it tends to have a reflexive or passive meaning. For example, اِنْكَسَرَ 'to be broken’ (from كَسَرَ ‘to break’), اِنْفَجَرَ 'to explode (intransitive)’ (from فَجَرَ ‘to explode (transitive)’).
This verb form is created by infixing ـتَـ after the first root consonant, and prefixing اِ when there is no other prefix added to the verb. It often has a reflexive or passive meaning, e.g. اِشْتَهَرَ 'to be famous’, اِشْتَغَلَ 'to occupy oneself’.
This is a rare form that mostly occurs with a few verbs that describe color and physical defects, for example اِبْيَضَّ 'to turn white’ (from 'white’).
This verb form is created by dropping the first vowel of form I and prefixing it with سْتَـ or اِستَـ . These verbs often have a meaning related to requesting or seeking something. For example استفهم 'to inquire’ (from فهم 'to understand’), استكتب 'to ask (somebody) to write’ (from كتب 'to write’).
This is a rare form with a similar meaning to form XI. For example اِخْضَارَّ 'to turn green' (from 'green').
This is a very rare form which only occurs in a few verbs, for example اِحْدَوْدَقَ 'to surround'.
This is a very rare form which only occurs in a few verbs, for example اِخْرَوَّطَ 'to get entangled'.
This is the most basic form for verbs with four-letter roots. It is often derived from a related Arabic noun. For example, تَرْجَمَ 'to translate', تَلْفَنَ 'to telephone', وَسْوَسَ 'to whisper'.
These are often reflexive and have a similar meaning to verbs in form V. For example, تَمَرْكَزَ 'to be stationed', تَزَلْزَلَ 'to shake'.
This is a very rare form which only occurs in a few verbs, for example اِجْرَنْثَمَ 'to adhere'.
This verb form is uncommon and usually has an intransitive meaning, for example اِضْمَحَلَّ 'to decay'.
The common negation verb لَيْسَ 'to not be' only exists in the past tense.