              Both claims have come in for criticism, and each surely  requires  defense.[15] Aristotle offers neither conviction a defense in his Categories. Nor, indeed, does he offer any principled grounding for just these categories of being, a circumstance which has left him open to further criticism from later philosophers, including famously Kant who, after lauding Aristotle for coming up with the idea of category theory, proceeds to excoriate him for selecting his particular categories on no principled basis whatsoever. Kant alleges that Aristotle picked his categories of being just as he happened to stumble upon them in his reveries (Critique of Pure Reason, A81/B107).   According to Kant, then, Aristotle’s categories are ungrounded.  Philosophers and scholars both before and after Kant have sought to provide the needed grounding, whereas Aristotle himself mainly tends to justify the theory of categories by putting it to work in his various philosophical investigations.