The science of the Arabic language known as نحو – basically translated as Arabic grammar and Arabic syntax – is a topic through which we learn to correctly convey meaning in Arabic, form coherent sentences, and protect ourselves from verbal error. Where Lexicology and Arabic Morphology are concerned with being able to work with the internals of words, Arabic grammar is concerned with being able to work with the endings of words in order to read and comprehend in a sentential milieu.
Arabic grammar (نحو /naḥw/) is centered around a single topic; grammatical inflection. Anything studied in the language is studied only because it relates to this issue. It is a feat of staggering genius on the part of medieval grammarians that almost all aspects of the Arabic language are covered just by concentrating on the issue of grammatical inflection. In studying the rules of Arabic grammar, we start with this topic, and it branches out to cover the entire language.