Overview of Arabic Words
We divide words in Arabic into three self-contained categories as follows.
اِسْم: (usually translated as “nouns”) includes nouns, pronouns, adjectives, adverbs, etc
حَرْف: particles, articles, and conjunctions
Particles are completely unpredictable; they don’t fall into the templatic system (i.e. they have no patterns) nor do they undergo any morphophonemic changes. They are what they are and must be memorized. The up side is that there are relatively few of them in the language – within one hundred.
Nouns and verbs do fall into the templatic system and have very systematic morphophonemic rules that govern them. This includes the study of how verbs are conjugated, how they move from pattern to pattern to enhance their meanings, how the participles and other nouns are derived, how nouns pluralize, etc.