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Shiavault - a Vault of Shia Islamic Books Logic in the Islamic Legacy: a General Overview Domains of Logic The Subject Matter of Logic Al-Farabi, in his Ihsa' al-'ulum (Enumeration of the Sciences), defines logic as an instrumental, rule-based science aimed at directing the intellect towards the truth and safeguarding it from error in its acts of reasoning.

He states: The subject matters ( mawdû‘ât ) of logic are the things for which [logic] provides the rules, namely, intelligibles in so far as they are signified by expressions, and expressions in so far as they signify intelligibles.

He defends the need for such a science of reasoning on the grounds that it is possible for the mind to err in at least some of its acts, for example, in those in which the intelligibles sought are not innate, but are rather attained discursively and empirically 'through reflection and contemplation'. Al-Farabi compares logic to tools such as rulers and compasses, which are used to ensure exactness when we measure physical objects subject to the errors of sensation.

Like these tools, logical measures can be employed by their users to verify both their own acts of reasoning and the arguments of others. Indeed, logic is especially useful and important to guide the intellect when it is faced with the need to adjudicate between opposed and conflicting opinions and authorities. Al-Farabi's view of logic as a rule-based science which governs the mind's operations over intelligibles forms the foundation for Ibn Sina's later refinements.

In the opening chapters of his al-Madkhal (Introduction), the first logical book of his encyclopedic work al-Shifa' (Healing), Ibn Sina describes the purpose of logic as one of enabling the intellect to acquire 'knowledge of the unknown from the known'. He defends the need for logic by arguing that the innate capacities of reasoning are insufficient to ensure the attainment of this purpose, and thus they require the aid of an art.

While there may be some cases in which innate intelligence is sufficient to ensure the attainment of true knowledge, such cases are haphazard at best; he compares them to someone who manages to hit a target on occasion without being a true marksman. The most important and influential innovation that Ibn Sina introduces into the characterization of logic is his identification of its subject matter as 'second intentions' or 'secondary concepts', in contrast to 'first intentions'.