As in other Semitic languages, Arabic has a complex and unusual morphology (i.e. method of constructing words from a basic root). Arabic has a nonconcatenative "root-and-pattern" morphology: A root consists of a set of bare consonants (usually three), which are fitted into a discontinuous pattern to form words. For example, the word for 'I wrote' is constructed by combining the root k-t-b 'write' with the pattern -a-a-tu 'I Xed' to form katabtu 'I wrote'. Other verbs meaning 'I Xed' will typically have the same pattern but with different consonants, e.g. qaraʼtu 'I read', akaltu 'I ate', dhahabtu 'I went', although other patterns are possible (e.g. sharibtu 'I drank', qultu 'I said', takallamtu 'I spoke', where the subpattern used to signal the past tense may change but the suffix -tu is always used).

From a single root k-t-b, numerous words can be formed by applying different patterns: