Logic as the Instrument of All Philosophy

Avicenna follows al-Farabi in treating logic as an instrumental or propaedeutic discipline: it does not tell us what is true about the world but gives us the tools for discovering and demonstrating truth. The central tool is the syllogism — the structured argument in which a conclusion is drawn necessarily from premises. Avicenna's account of the syllogism is more systematic than Aristotle's original formulation, and he added significant original work on hypothetical and disjunctive syllogisms that the Greek tradition had left underdeveloped.

Before syllogistic argument, the mind must have concepts — clear, well-defined ideas of what things are. Avicenna's account of concept formation draws on his epistemology of abstraction: the mind strips away the particular, material, and accidental features of experienced things to arrive at the universal form. A concept is genuine when it captures the essential nature of its object — what the thing necessarily and always is — and this is achieved through the process of definition: identifying the genus and differentia that jointly specify the essence. Avicenna's Book of Knowledge presents this logical method in Persian for the first time, making systematic philosophy accessible to a reading public that lacked Arabic.

One of Avicenna's most influential logical claims is that "being" (wujud, existence) is the first concept that the mind grasps — the concept presupposed by all other concepts, the one that cannot be defined because everything else is defined in terms of it. "Being" is known, in a sense, immediately and without derivation: one cannot not know what it means for something to exist, even though this knowledge resists explicit definition. This doctrine of the primacy of being — taken up by Aquinas as the claim that "ens" is the first object of the intellect — gave Avicenna's logic a metaphysical foundation that shaped the entire subsequent tradition of Islamic and Scholastic philosophy.

The Book of Knowledge (Danishnama-i 'Ala'i) opens with a logic section that draws on and summarises Avicenna's much longer treatment of logic in the Book of Healing. The claim that being is the primary concept of the intellect is developed in the Ilahiyyat (Metaphysics) of the Book of Healing, Book I, chapter 5, and influenced Aquinas's doctrine of the primacy of ens in De Veritate.