 The view that both propositions and non-propositional concepts can be true runs fairly deep in al-Fārābī’s thinking, although he recognizes that not everybody agrees with it ([Commentary on De Interpretatione] 52.13f). For example, this view allows him to think of definition of non-propositional concepts and demonstration of propositions as overlapping procedures; there can be definitions that are identical with demonstrations except in the order of their parts ([Demonstration]  47.11).[22]  Avicenna a hundred years later found it essential to distinguish between non-propositional and propositional concepts. Provocatively he used al-Fārābī’s own terminology of taṣawwur and taṣdīq to fix the distinction; for Avicenna any concept can be conceptualized, but only propositions can go on to be  verified.[23] 