“The controversy as to whether socialism is possible has been settled by the fact that it exists, and it is a fundamental axiom of my philosophy, at any rate, that anything that exists, is possible.”

The Ecological Vision: Reflections on the American Condition (1993)
1990s and later

"Totalitarianism and the Virtue of the Lie", as quoted in Is God Happy? Selected Essays (2013), Basic Books, p. 57

Source: Guide for the Perplexed (c. 1190), Part III, Ch.20

Source: 1850s, An Investigation of the Laws of Thought (1854), p. 50

Slowness (1995)

In Search of the Miraculous (1949)

[O] : Introduction, 0.6
Semiotics and the Philosophy of Language (1984)
Context: When semiotics posits such concepts as 'sign', it does not act like a science; it acts like philosophy when it posits such abstractions as subject, good and evil, truth or revolution. Now, a philosophy is not a science, because its assertions cannot be empirically tested … Philosophical entities exist only insofar as they have been philosophically posited. Outside their philosophical framework, the empirical data that a philosophy organizes lose every possible unity and cohesion.
To walk, to make love, to sleep, to refrain from doing something, to give food to someone else, to eat roast beef on Friday — each is either a physical event or the absence of a physical event, or a relation between two or more physical events. However, each becomes an instance of good, bad, or neutral behavior within a given philosophical framework. Outside such a framework, to eat roast beef is radically different from making love, and making love is always the same sort of activity independent of the legal status of the partners. From a given philosophical point of view, both to eat roast beef on Friday and to make love to x can become instances of 'sin', whereas both to give food to someone and to make love to у can become instances of virtuous action.
Good or bad are theoretical stipulations according to which, by a philosophical decision, many scattered instances of the most different facts or acts become the same thing. It is interesting to remark that also the notions of 'object', 'phenomenon', or 'natural kind', as used by the natural sciences, share the same philosophical nature. This is certainly not the case of specific semiotics or of a human science such as cultural anthropology.

Source: Vestiges of the Natural History of Creation (1844), p. 388

Motto of the work written by Hesse, and attributed to an "Albertus Secundus"
The Glass Bead Game (1943)
Context: For although in a certain sense and for light-minded persons non-existent things can be more easily and irresponsibly represented in words than existing things, for the serious and conscientious historian it is just the reverse. Nothing is harder, yet nothing is more necessary, than to speak of certain things whose existence is neither demonstrable nor probable. The very fact that serious and conscientious men treat them as existing things brings them a step closer to existence and to the possibility of being born.