 Large parts of both [Expressions] and [Letters] are devoted to explaining how we can elicit philosophical information by asking these and similar  questions.[10]  Thus for each primary concept we can ask “What is it”? Al-Fārābī defines the genus (jins) of the concept to be the answer to this question. By asking “which thing” (in that genus), we get a more specific description that provides the species (naw‘) below the genus. Al-Fārābī explains how further questions can elicit the differentiae and the definitions of concepts. The “essence” (dhāt) of a concept consists of the concepts included in the definition of the concept; these concepts in the essence are also described as “constitutive” (muqawwim) for the concept. 