The unity considered to be between a subject and predicate...

The unity considered to be between a subject and predicate sometimes is a conceptual unity, such as, “Man is human,” and sometimes it is a unity of instance, such as, “Man searches for truth,” in which the subject and predicate do not have a conceptual unity, but they are united by instance. The first kind is called “primary predication” ( ḥaml awwalī ) and the second kind is called “common predication” ( ḥaml shāyi‘ ).

In common predication the predicate of the proposition is ‘existent’ or the equivalent, and the proposition is termed a ‘simple question’ ( halliyyah basīṭah ) whereas in other cases it is termed a ‘compound question’ ( halliyyah murakkabah ).

1 The first is like, “Man is an existent,” and the second like, “Man searches for truth.” The acceptance of simple questions depends on this, the concept of “existence” must be accepted in terms of a independent concept which may be predicated (predicative concept). But most of the Western philosophers accept the concept of existence only as a nominal concept which is not independent. Discussion of this may be found in the part on ontology.

In compound questions, if the concept of the predicate is obtained through analysis of the concept of the subject, the proposition is called ‘analytic’, and otherwise it is called ‘synthetic’. For example, the proposition, “All children have fathers,” is analytic, for when the concept of child is analyzed, the concept of father is obtained from it.

But the proposition, “Metals expand when heated,” is synthetic, for from the analysis of the meaning of ‘metal’ we cannot obtain the concept of expansion. In the same way, the proposition, “All men have fathers,” is synthetic, for from the analysis of the meaning of ‘man’ the concept of ‘having a father’ is not obtained. Also, “Every effect requires a cause,” is analytic, and “All existents require a cause,” is synthetic.

It must be noted that Kant has divided the synthetic propositions into two kinds, a priori and a posteriori , and considers mathematical propositions to belong to the former. However, some positivists attempt to reduce them to analytic propositions. In classical logic, propositions are divided into self-evident and theoretical (non-self-evident).

Propositions are self-evident whose affirmation does not require thinking and reasoning, while theoretical propositions are those whose affirmation requires thinking and reasoning.