““You can prove anything you want by coldly logical reason—if you pick the proper postulates. We have ours and Cutie has his.”
“Then let’s get at those postulates in a hurry. The storm’s due tomorrow.”
Powell sighed wearily. “That’s where everything falls down. Postulates are based on assumptions and adhered to by faith. Nothing in the Universe can shake them. I’m going to bed.””

If This Goes On— (p. 432)
Short fiction, The Past Through Tomorrow (1967)

Source: The Blind Watchmaker (1986), Chapter 11 “Doomed Rivals” (p. 316)

The Doctrine of Necessity Examined (1892)
Context: When I have asked thinking men what reason they had to believe that every fact in the universe is precisely determined by law, the first answer has usually been that the proposition is a "presupposition " or postulate of scientific reasoning. Well, if that is the best that can be said for it, the belief is doomed. Suppose it be " postulated " : that does not make it true, nor so much as afford the slightest rational motive for yielding it any credence. It is as if a man should come to borrow money, and when asked for his security, should reply he "postulated " the loan. To "postulate" a proposition is no more than to hope it is true. There are, indeed, practical emergencies in which we act upon assumptions of certain propositions as true, because if they are not so, it can make no difference how we act. But all such propositions I take to be hypotheses of individual facts. For it is manifest that no universal principle can in its universality be compromised in a special case or can be requisite for the validity of any ordinary inference.

The Autocrat of the Breakfast Table (1858)

Journals of Søren Kierkegaard 1A75, 1835
1830s, The Journals of Søren Kierkegaard, 1830s

Source: 1910s, Introduction to Mathematical Philosophy (1919), Ch. 7: Rational, Real and Complex Numbers

Speech to the annual meeting of the Union of Girls' Schools (27 October 1927), quoted in Our Inheritance (London: Hodder and Stoughton, 1938), pp. 150-151.
1927
Context: Your work in social service, whatever form it may take, requires exactly those two things that my work requires... patience and faith in human worth. Those are the real foundations of democracy, not equality in the sense in which that word is so often used. We are not all equal, and never shall be; the true postulate of democracy is not equality but the faith that every man and woman is worth while.

The God Delusion (2006)
Context: If the alternative that's being offered to what physicists now talk about - a big bang, a spontaneous singularity which gave rise to the origin of the universe - if the alternative to that is a divine intelligence, a creator, which would have to have been complicated, statistically improbable, the very kind of thing which scientific theories such as Darwin's exists to explain, then immediately we see that however difficult and apparently inadequate the theory of the physicists is, the theory of the theologians - that the first course was a complicated intelligence - is even more difficult to accept. They're both difficult but the theory of the cosmic intelligence is even worse. What Darwinism does is to raise our consciousness to the power of science to explain the existence of complex things and intelligences, and creative intelligences are above all complex things, they're statistically improbable. Darwinism raises our consciousness to the power of science to explain how such entities - and the human brain is one - can come into existence from simple beginnings. However difficult those simple beginnings may be to accept, they are a whole lot easier to accept than complicated beginnings. Complicated things come into the universe late, as a consequence of slow, gradual, incremental steps. God, if he exists, would have to be a very, very, very complicated thing indeed. So to postulate a God as the beginning of the universe, as the answer to the riddle of the first cause, is to shoot yourself in the conceptual foot because you are immediately postulating something far far more complicated than that which you are trying to explain. Now, physicists cope with this problem in various ways, which may seem somewhat unconvincing. For example, they suggest that our universe is but one bubble in foam of universes, the multiverse, and each bubble in the foam has a different set of laws and constants. And by the anthropic principle we have to be - since we're here talking about it - in the kind of bubble, with the kind of laws and constants, which are capable of giving rise to the evolutionary process and therefore to creatures like us. That is one current physicists' explanation for how we exist in the kind of universe that we do. It doesn't sound so shatteringly convincing as say Darwin's own theory, which is self-evidently very convincing. Nevertheless, however unconvincing that may sound, it is many, many, many orders of magnitude more convincing than any theory that says complex intelligence was there right from the outset. If you have problems seeing how matter could just come into existence - try thinking about how complex intelligent matter, or complex intelligent entities of any kind, could suddenly spring into existence, it's many many orders of magnitude harder to understand.

Lynchburg, Virginia, 23/10/2006 http://www.youtube.com/watch?v=qR_z85O0P2M&t=42m41s

Emphatic capitalization in original.
The Unreasonable Effectiveness of Mathematics (1980)