“The majority of them seem to be "sub-critical," i.e., to correspond in this analogy to piles of sub-critical size. An idea presented to such a mind will on average give rise to less than one idea in reply. A smallish proportion are super-critical. An idea presented to such a mind may give rise to a whole "theory" consisting of secondary, tertiary and more remote ideas.”

"On Freedom" in All Life is Problem Solving (1999)
Context: When I speak of reason or rationalism, all I mean is the conviction that we can learn through criticism of our mistakes and errors, especially through criticism by others, and eventually also through self-criticism. A rationalist is simply someone for whom it is more important to learn than to be proved right; someone who is willing to learn from others — not by simply taking over another's opinions, but by gladly allowing others to criticize his ideas and by gladly criticizing the ideas of others. The emphasis here is on the idea of criticism or, to be more precise, critical discussion. The genuine rationalist does not think that he or anyone else is in possession of the truth; nor does he think that mere criticism as such helps us achieve new ideas. But he does think that, in the sphere of ideas, only critical discussion can help us sort the wheat from the chaff. He is well aware that acceptance or rejection of an idea is never a purely rational matter; but he thinks that only critical discussion can give us the maturity to see an idea from more and more sides and to make a correct judgement of it.

Je m’entretiens avec moi-même de politique, d’amour, de goût ou de philosophie ; j’abandonne mon esprit à tout son libertinage ; je le laisse maître de suivre la première idée sage ou folle qui se présente … Mes pensées ce sont mes catins.
Variant translations:
My ideas are my whores.
My thoughts are my trollops.
Rameau's Nephew (1762)

Source: The Meaning of a Liberal Education (1926), p. 183

De Abaitua interview (1998)
Context: To me, when we talk about the world, we are talking about our ideas of the world. Our ideas of organisation, our different religions, our different economic systems, our ideas about it are the world. We are heading for a radical revision where you could say we are heading towards the end of the world, but more in the R. E. M. sense than the Revelation sense. That is what apocalypse means – revelation. I could square that with the end of the world, a revelation, a new way of looking at things, something that completely radicalises our notions of the where we were, when we were, what we were, something like that would constitute an end to the world in the kind of abstract – yet very real sense – that I am talking about. A change in the language, a change in the thinking, a change in the music. It wouldn’t take much – one big scientific idea, or artistic idea, one good book, one good painting – who knows – we are at a critical point where the ideas are coming thicker and faster and stranger and stranger than they ever were before. They are realised at a greater speed, everything has become very fluid.

Source: How to Solve It (1945), p. 100

Original: Avere buone idee è fondamentale per il successo di qualsiasi lavoro creativo.
Source: prevale.net

Remarks Recorded for the Opening of a USIA Transmitter at Greenville, North Carolina (8 February 1963) Audio at JFK Library (01:29 - 01:40) http://www.jfklibrary.org/Asset-Viewer/Archives/JFKWHA-161-010.aspx · Text of speech at The American Presidency Project http://www.presidency.ucsb.edu/ws/?pid=9551
1963
Variant: A man may die, nations may rise and fall, but an idea lives on. Ideas have endurance without death.

Source: The Golden Bough (1890), Chapter 4, Magic and Religion.

Source: "From Enlightenment to Revolution" (1975), p. 260
Context: But it is useless to subject this hash of uncritical language to critical questioning. We can make no sense of these sentences of Engels unless we consider them as symptoms of a spiritual disease. As a disease, however, they make excellent sense for, with great intensity, they display the symptoms of logophobia, now quite outspokenly as a desperate fear and hatred of philosophy. We even find named the specific object of fear and hatred: it is "the total context of things and of knowledge of things." Engels, like Marx, is afraid that the recognition of critical conceptual analysis might lead to the recognition of a "total context," of an order of being and perhaps even of cosmic order, to which their particular existences would be subordinate. If we may use the language of Marx: a total context must not exist as an autonomous subject of which Marx and Engels are insignificant predicates; if it exists at all, it must exist only as a predicate of the autonomous subjects Marx and Engels. Our analysis has carried us closer to the deeper stratum of theory that we are analysing at present, the meaning of logophobia now comes more clearly into view. It is not the fear of a particular critical concept, like Hegel's Idea, it is rather the fear of critical analysis in general. Submission to critical argument at any point might lead to the recognition of an order of the logos, of a constitution of being, and the recognition of such an order might reveal the revolutionary idea of Marx, the idea of establishing a realm of freedom and of changing the nature of man through revolution, as the blasphemous and futile nonsense which it is.