In English, words are either singular or plural, yet in Arabic, words can be singular (مفرد), dual (مثنى) or plural (جمع). Singular words refer to one person or thing only, dual nouns refer to two persons or things, while plural words refer to more than two. It is often the case that learners of Arabic miss the dual and treat it like plural. Therefore, one must be very careful about identifying the dual.

Dual nouns are marked with the suffix (ان) which is sometimes written as (ين), e.g. (رجل) “man” is singular, (رجلان) or (رجلين) “two men” is dual. In feminine words ending in (ة), it has to be changed into (ت) when a word becomes dual, e.g. (امرأة) “woman” is singular, (امرأتان) or (امرأتين) “two women” is dual. Adjectives have to agree with the nouns they modify in number, so adjectives must take the dual ending like nous, e.g. (كتابان كبيران) or (كتابين كبيرين) “two big books”.

Plural nouns are sometimes marked by suffixes (الجمع السالم) “sound plural” or by changing the form of the word (جمع التكسير) “broken plural”. Sound masculine plurals are formed by adding the suffix (ون) which is sometimes written as (ين), e.g. (مهندسون) or (مهندسين) “engineers”. Sound feminine plurals are formed by adding the suffix (ات) which, e.g. (مهندسات) “engineers”. Broken plurals are formed by changing the form of the word, e.g. the plural of (طالب) “student” is (طلاب) “students”. There is no rule to specify which word has a sound plural and which one has a broken plural. However, it may be useful to for learners of Arabic to learn the broken plurals as soon as they are encountered.

Adjectives of plural nouns are usually plural as well, e.g. (مهندسون أمريكيون) and (مهندسات أمريكيات) “American engineers”. It should be noted that words that refer to non-humans are treated like singular feminine in agreement, so “American universities” is (جامعات أمريكية). Although universities is plural, it does not refer to a human, and therefore the adjectives that goes with it is singular feminine.