Distinction, the fundamental philosophical abstraction, involves the recognition of difference.
The merely logical or virtual distinction, such as the difference between concavity and convexity, involves the mental apprehension of two definitions, but which cannot be realized outside the mind, as any concave line would be a convex line considered from another perspective.
[3] Some relevant distinctions to the history of Western philosophy include: While there are anticipation of this distinction prior to Kant in the British Empiricists (and even further in Scholastic thought), it was Kant who introduced the terminology.
Saul Kripke was the first major thinker to propose that there are analytic a posteriori knowledge claims.
[5] In Kant, the distinction between appearance and thing-in-itself is foundational to his entire philosophical project.