in linguistics, one of several methods for creating the stems, or most elementary forms, of words. The root and pattern system is found in the Afro-Asiatic language (Afro-Asiatic languages) phylum, and particularly in the Semitic (Semitic languages) branch of the phylum.

The root is a set of consonants arranged in a specific sequence; it identifies the general realm of the word's meaning. Additional information, such as part of speech and tense, is reflected in the stem's vocalic (vowel) and syllabic features, called the pattern.

A given set of stems may thus be distinguished by either the pattern or the root. In the first case the stems have a common root and thus share a common semantic field, as with the English verbs write, wrote, and written. These three verbs share the root wr-t(t)- (parenthetical letters reflect an optional feature) and are differentiated by the patterns -i-, -o-, -i-en, which indicate tense. Alternatively, these patterns could be combined with a different root, such as r-s-, for rise, rose, and risen; the tenses parallel those in the first case, but the semantic field of the series has changed.

Although these examples illustrate the root and pattern system to some extent, the lexical sense in most European languages resides primarily in the stem. The grammatical information is thus found in prefixes, suffixes, or infixes: washed is created by combining the stem wash- with the past tense-suffix -ed, while washer is created by combining the stem and the agent-suffix -er.

In contrast, stems in the Semitic languages indicate different grammatical contexts by using the root and pattern system and as a result can appear in quite different shapes. Compare, for instance, the many variants on the Arabic (Arabic language) root k-t-b-: the past stem (active) katab-, as in katab-tu ‘I wrote'; the past stem (passive) kutib-, as in kutib-a ‘it was written'; the present stem (active) -ktub-, as in ʾa-ktub-u ‘I write'; and the active participial stem kātib-, as in kātib-un ‘writing 【one】.'