ASSERTIVE FUNCTION (Latin assertio, from asserere—to assert)—in the philosophy of knowledge, the assertive function is one of three functions of “is” in judgments (beside the affirmative and cohesive functions). It is the ordering of an entire statement to the state of affairs it designates (a strictly indicated relation which occurs in the judgment between the system of subject-predicate concepts joined by the cohesive function of “is” and reality itself conceived under the aspect of this system). It formally creates a judgment. The effect of the assertive function is a cognitive assertion.
By virtue of the assertive function, the proposition-judgment copula “is” is predicative judgments not only equates the predicate with the subject and joins them into one statement (the cohesive function of “is”), but with concomitant reflection it equates the whole thus produced with an objective state of affairs. The assertive function is an essential function for judgmental cognition. By the assertive function, judgmental cognition contains new cognitive information—the assertion of identity in being between the subject and predicate—a judgments are new inspections of reality that differ from concepts and are essentially one and incomposite (even though a few components occur in them).
By the “is” in its assertive function, a judgment asserts that two different concepts as concepts are identified in one and the same thing. The ordering that occurs in this way of the statement to the designated state of affairs, and the perception and recognition of agreement or disagreement of the statement with reality itself, are the reason for the truth or falsehood of the judgment. Hence the assertive function is sometimes called the truth function. By it the intellect makes itself aware, with the participation of concomitant reflection that equates the entire statement of judgment to the real state, that a thing is such as is the concept concerning it. The assertive function expresses the subjective mode of the cognitive grasp of reality in a judgment and it places a statement in the field of truth and falsehood.
The assertive function is essential for cognition of truth. It is a relation of agreement (or disagreement) of the whole of a statement of judgment with an object state of affairs and presupposes a prior affirmative function of “is” (a function proper to existential judgments). This prior function is in direct contact with reality. It grasps the existence of the thing itself and is the epistemic reason for the realism of all other acts of cognition (it is implicit in them).
In logic, the affirmative function is the function p, one of two besides negation (the function not p, the simplest truth function in which only one argument occurs. The logical value of the assertive function is identical with the logical value of an argument.
J. M. Bocheński, Formale Logik, Fr 1956; Krąpiec Dz [Works] II; J. Pelc, O wartości logicznej i charakterze asertywnym zdań w dziele literackim [On the logical value and assertive character of proposition in a literary work]; Estetyka [Aesthetics] I (1960), 97–128; K. Ajdukiewicz, Logika pragmatyczna, Wwa 1965, 19742; S. Majdański, Problem asercji zdaniowej [The problem of propositional assertion], Lb 1972; Krąpiec, Dz [Works] XIII.