except in the mind—as in the division of animals into rational and non-rational beings, and of nouns into inflected and indeclinable nouns. What is divided here is a universal intellectual concept, which is universal only in the mind.

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The term harf refers to meaningful particles, which constitute a category alongside nouns and verbs. Examples include prepositions, jussive particles, the two future particles, and particles resembling verbs, such as inna and its sister particles. These particles have well-known classifications in works on Arabic grammar. For example, grammarians classify them, with respect to inflection, into those specific to nouns and those specific to verbs. They say:

“A particle specific to either category, without being like a part of the word itself, governs inflection.”

Thus, prepositions and inna and its sister particles govern nouns, while subjunctive and jussive particles govern verbs. This contrasts with the definite article and the two future particles, sa- and sawfa, which do not govern inflection because they are like parts of the word itself.

They also say:

“By analogy, mā (‘not’) should not govern inflection, because it introduces both nominal and verbal sentences. The people of the Hijaz, however, made it govern inflection because of its resemblance to laysa (‘is not’).”

The Quran follows their usage in His words:

“This is no human being.”

“They are not their mothers.”