Full Idea
Metaphysics can be ...the investigation of everything that can ever be cognized a priori, as well as the presentation of that which constitutues a system of pure philosophical cognitions of this kind.
Gist of Idea
Metaphysics is a systematic account of everything that can be known a priori
Source
Immanuel Kant (Critique of Pure Reason [1781], B869/A841)
Book Reference
Kant,Immanuel: 'Critique of Pure Reason', ed/tr. Guyer,P /Wood,A W [CUO 1998], p.969
A Reaction
[He excludes mathematics from this] Moore says this is Kant's most interesting definition of metaphysics (among several versions).