Metaphysics

[Pragmatism] will serve to show that almost every proposition of ontological metaphysics is either meaningless gibberish,—one word being defined by other words, and they by still others, without any real conception ever being reached,—or else is downright absurd. (Peirce, "What Pragmatism Is")

The fundamental faith of the metaphysicians is the faith in opposite values.… one may doubt, first, whether there are any opposites at all, and secondly whether these … opposite values … are not perhaps merely foreground estimates, only provisional perspectives, perhaps even from some nook, perhaps from below. (Nietzsche, section 2)

The non-theoretical character of metaphysics would not be in itself a defect.… the danger lies in the deceptive character of metaphysics; it gives the illusion of knowledge without actually giving any knowledge. This is why we reject it. (Carnap, "The Rejection of Metaphysics," from Philosophy and Logical Syntax, 1934, section 5)