«And yet, the whole importance of the refutation of received opinion, or of the best scientific opinion or idea or proposal is just this: refutation opens the road to innovation. Nothing is a more potent heuristic than refutation. Nothing is more conductive to progress than criticism of the current situation, nothing more likely to herald the new than discontent with the old. Criticism is liberation.
The positive power of negative thinking.
Nor is this all. We can criticize science by attempting to empirically refute its doctrines; we can criticize metaphysics by showing its poverty; we can criticize a research program by finding and criticizing the comprehensive system — the metaphysics — behind it. And criticism opens the way to the introduction of an alternative to whatever was criticized, and vice versa.»
Joseph Agassi, «Sir Karl Popper in Retrospect — the positive power of negative thinking», can be found in «The Gentle Art of Philosophical Polemics».