 Broadly following Aristotle, al-Fārābī adds to noun and particle a third class, namely verb (kalima). A verb simultaneously expresses three pieces of meaning: a simple primary concept, a copular linking, and a tense (and hence a time). Thus in “Zayd walked”, the verb “walked” expresses (i) the primary concept “walking”, (ii) a linking of this concept to the concept of Zayd, and (iii) a past tense. 