No single theory ever agrees with all the facts in its domain. — Theory

"When a theory is transformed into an ideology, it begins to destroy the self and self-knowledge. Originally born of feeling, it pretends to float above and around feeling. Above sensation. It organizes experience according to itself, without touching experience. By virtue of being itself, it is supposed to know. To invoke the name of this ideology is to confer truthfulness. No one can tell it anything new. Experience ceases to surprise it, inform it, transform it. It is annoyed by any detail which does not fit into its world view. Begun as a cry against the denial of truth, now it denies any truth which does not fit into its scheme. Begun as a way to restore ones sense of reality, now it attempts to discipline real people, to remake natural beings after its own image. All that it fails to explain it records as its enemy. Begun as a theory of liberation, it is threatened by new theories of liberation; it builds a prison for the mind."

"All competent thinkers agree with Bacon that there can be no real knowledge except that which rests upon observed facts. This fundamental maxim is evidently indisputable if it is applied, as it ought to be, to the mature state of our intelligence. But, if we consider the origin of our knowledge, it is no less certain that the primitive human mind could not, and indeed ought not to, have thought in that way. For if, on the one hand, every Positive theory must necessarily be founded upon observations, it is, on the other hand, no less true that, in order to observe, our mind has need of some theory or other. If in contemplating phenomena we did not immediately connect them with principles, not only would it be impossible for us to combine these isolated observations, and therefore to derive profit from them, but we should even be entirely incapable of remembering facts, which would for the most remain unnoted by us. Thus there were two difficulties be overcome: the human mind had to observe in order to form real theories, and yet had to form theories of some sort before it could apply itself to a connected series of observations. The primitive human mind, therefore, found itself involved in a vicious circle, from which it would never have had any means of escaping, if a natural way of the difficulty had not fortunately found by the spontaneous development of Theological conceptions. ...chimerical hopes ..exaggerated ideas of mans importance in the universe to which the Theological Philosophy ...at the commencement, ...afforded an indispensable stimulus without the aid which we cannot, indeed, conceive how the primitive human mind would have been induced to undertake any arduous labours."

"When an active individual of sound common sense perceives the sordid state of the world, desire to change it becomes the guiding principle by which he organizes given facts and shapes them into a theory. The methods and categories as well as the transformation of the theory can be understood only in connection with his taking of sides. This, in turn, discloses both his sound common sense and the character of the world. Right thinking depends as much on right willing as right willing on right thinking."

"Practical life is not necessarily directed toward other people, as some think; and it is not the case that practical thoughts are only those which result from action for the sake of what ensues. On the contrary, much more practical are those mental activities and reflections which have their goal in themselves and take place for their own sake."

"I learned about renormalization theory as a graduate student, mostly by reading Dyson’s papers. ... From the beginning it seemed to me to be a wonderful thing that very few quantum field theories are renormalizable. Limitations of this sort are, after all, what we most want, not mathematical methods which can make sense of an infinite variety of physically irrelevant theories, but methods which carry constraints, because these constraints may point the way toward the one true theory."

"It is clear that the arm of criticism cannot replace the criticism of arms. Material force can only be overthrown by material force, but theory itself becomes a material force when it has seized the masses. Theory is capable of seizing the masses when it demonstrates ad hominem, and it demonstrates ad hominem as soon as it becomes radical. To be radical is to grasp things by the root. But for man the root is man himself. What proves beyond doubt the radicalism of German theory, and thus its practical energy, is that it begins from the resolute positive abolition of religion. The criticism of religion ends with the doctrine that man is the supreme being for man. It ends, therefore, with the categorical imperative to overthrow all those conditions in which man is an abased, enslaved, abandoned, contemptible being—conditions which can hardly be better described than in the exclamation of a Frenchman on the occasion of a proposed tax upon dogs: Wretched dogs! They want to treat you like men!"