How numbers behave

A famously messy corner of Arabic grammar. Reverse-gender threes-through-tens, accusative singulars after eleven, and a different agreement for hundreds and thousands.

If there is a single rule of Arabic grammar that even advanced learners get wrong, it is the agreement of numbers with the things they count. The numbers themselves are easy enough to learn. What they do to the noun next to them, and how they themselves are gendered, is unlike anything in English. The system is not arbitrary — it has a logic — but the logic is layered, and the layers do not align with English speakers' intuitions. Most people learn each tier of the system separately and stitch them together with practice.

One and two

One is a normal adjective. It follows the noun and agrees with it.

Two is not a separate word — it is the dual ending on the noun (-aan):

If you want to emphasize the "two-ness," you can also use the word ithnaan (m.) or ithnataan (f.) as an apposition: kitaabaan ithnaan, "two books." This is uncommon in plain prose.

Three through ten — reverse gender

This is the famously perverse rule. With numbers from three to ten:

• The counted noun is plural and in the genitive.
• The number itself takes the opposite gender from the singular of the noun. A masculine singular noun (with a masculine plural) takes the feminine form of the number; a feminine singular noun takes the masculine form.

So you have a feminine "three" with a masculine plural noun, and a masculine "three" with a feminine plural noun. The asymmetry is genuine and has to be drilled.

The rule of thumb: look at the singular of the noun. If the singular is masculine (whatever its plural pattern), the number gets -a/-at (feminine ending). If the singular is feminine, the number is bare (masculine).

Eleven through nineteen — accusative singular

From 11 to 19, the rule changes. Here:

• The counted noun is singular, not plural.
• The counted noun is in the accusative.
• The number agrees in gender with the noun (no reversing) — except for the "ten" component of 13–19, which keeps reverse gender.

Twenty through ninety-nine

The decade words (20, 30, 40...) are invariable in gender. The unit before the decade (in numbers like 21, 22, 35) follows the rules above for its own range.

Hundreds, thousands, and beyond

For 100, 1000, and the larger words, the counted noun is singular genitive, in an idafa with the number:

The number 100 itself is mi'a; multiples of 100 are formed by prefixing the unit (thalaath mi'a, three hundred). 1000 is alf; multiples are similar (khamsat aalaaf, five thousand).

Be honest about the difficulty

This is the single most reliable pain point in Arabic grammar. Native speakers learn it late, and even highly literate Arabs occasionally mis-gender numbers in spontaneous speech. Spoken dialect dramatically simplifies the system: most colloquial varieties use a single form for each number, often skipping case endings, and pluralize the noun without much regard for the formal rules.

For practical purposes:

• Internalise the reverse-gender rule for 3–10 first. It comes up constantly.
• Know that 11+ takes a singular accusative noun. The exact case ending may not be pronounced, but the singular is.
• For hundreds and thousands, expect singular genitive (idafa).
• In dialect, listen first and copy.

Eight more in context

What it's called in the Arabic tradition

Numbers are الأَعْداد (al-aʿdaad). The thing counted is المَعْدود (al-maʿduud). The reverse-gender rule for 3–10 is المُخالَفَة (al-mukhaalafa, "the disagreement"). The peculiar rules for cardinal numbers are taught as a separate chapter in any classical Arabic grammar — under the heading العَدَد والمَعْدود (al-ʿadad wa-l-maʿduud, "the number and the counted").