The ease of knowing analytic propositions
Part of Kant’s argument in the Introduction to the Critique of Pure Reason involves arguing that there is no problem figuring out how knowledge of analytic propositions is possible.
To know an analytic proposition, Kant argued, one need not consult experience.
Instead, one need merely to take the subject and “extract from it, in accordance with the principle of contradiction, the required predicate…” (A7/B12)
In analytic propositions, the predicate concept is contained in the subject concept.
Thus, to know an analytic proposition is true, one need merely examine the concept of the subject. If one finds the predicate contained in the subject, the judgment is true.
Thus, for example, one need not consult experience to determine whether “All bachelors are unmarried” is true. One need merely examine the subject concept (“bachelors”) and see if the predicate concept “unmarried” is contained in it. And in fact, it is: “unmarried” is part of the definition of “bachelor,” and so is contained within it. Thus the proposition “All bachelors are unmarried” can be known to be true without consulting experience.
It follows from this, Kant argued, first:
– All analytic propositions are a priori; there are no a posteriori analytic propositions.
– It follows, second: There is no problem understanding how we can know analytic propositions. We can know them because we just need to consult our concepts in order to determine that they are true.
The possibility of metaphysics
After ruling out the possibility of analytic a posteriori propositions, and explaining how we can obtain knowledge of analytic a priori propositions, Kant also explains how we can obtain knowledge of synthetic a posteriori propositions.
That leaves only the question of how knowledge of synthetic a priori propositions is possible.
This question is exceedingly important, Kant maintains, as all important metaphysical knowledge is of synthetic a priori propositions.
If it is impossible to determine which synthetic a priori propositions are true, he argues, then metaphysics as a discipline is impossible.
The remainder of the Critique of Pure Reason is devoted to examining whether and how knowledge of synthetic a priori propositions is possible.