Classifying the words of a language into different categories is a matter of opinion, as different grammarians do it differently.
English grammars traditionally divide words into the following classes or parts of speech:
Arabic grammars use a different system which was described by Sibawayhi in the first chapter of his book. This system has three basic categories:
- ʔ·ismuṋ اِسْمٌ “name” (noun)
- Fiʕluṋ فِعْلٌ “action” (verb)
- Ħarfuṋ حَرْفٌ “word” (particle)
The ʔ·ism or noun category includes:
- Nouns (including the verbal nouns)
- Adjectives (including the verbal adjectives)
- Many adverbs
- Many prepositions
The “verbal noun” is a general designation for things such as the infinitives and gerunds, that is, noun forms that are automatically formed from verbs and which show some characteristics of verbs, such as the ability to govern an object or to be modified by an adverb. The corresponding category in Arabic is called Maṣdar مَصْدَرٌ “source,” which is a subcategory of the basic noun category.
The “verbal adjective” is a general designation for things such as the participles. It means adjectives that are automatically formed from verbs and which show some characteristics of verbs like the verbal nouns. The corresponding categories in Arabic grammar are the agent noun اِسْمُ الْفاعِلِ (active participle) and the patient noun اِسْمُ الْمَفْعُوْلِ (passive participle).
Any adverb or preposition that appears to be derived from a triconsonantal root is classified in the noun category.
In the Arabic system the word noun is ambiguous in that it can mean either a noun in the strict sense or an adjective (an adjective is a word that modifies a noun). The same ambiguity existed in ancient Greek and Latin grammars, which did not have a separate adjective category. In Latin grammars a noun proper was called nomen substantivum (substantive noun) and an adjective was called nomen adjectivum (adjective noun). In order to avoid ambiguity on this website, I will use the word substantive when I mean a noun in the narrow sense. Otherwise the word “noun” should be understood as including adjectives.
The fiʕl or verb category has only the “finite” verbs, i.e. the verb forms other than the verbal nouns and verbal adjectives.
The ħarf or particle category was defined by Sibawayhi as “meaningful words that are neither ʔ·ism nor fiʕl.” Words of this category are adverbs and prepositions that do not appear to be derived from triconsonantal roots.
The name of the ħarf category comes from Sibawayhi’s definition, which has the sentence ħarfuṋ ǵȃʔa li-maʕnaṋ حَرْفٌ جاءَ لِمَعْنًى . In this sentence the word ħarfuṋ means “a word,” which is a common meaning for this word in Classical Arabic but not in modern Arabic.