One question here is how such inference could ever yield new knowledge. Surely the conclusion must be somehow already contained in the premisses, if the premisses cannot be true where the conclusion is false. The second supposed activity of reason is the direct discovery of new truths. A truth that can be discovered by the activity of reason alone is called an a priori truth, and knowledge of it is a priori knowledge. One of the great questions in epistemology is how a priori knowledge is possible, and what sorts of truth can be known in this way.
Some propositions are true in virtue of their meaning alone, e.g. that all bachelors are people.
We know this truth, and not by appeal to the senses, to introspection, or to memory. So we know it by reason. They give us no substantial knowledge. We appear to be torn between saying that mathematical truths are important and saying that we know them by the activity of reason alone. It was the attempt to avoid this dilemma that led to Kant's first Critique .