The universe is a series of collapsed probabilities. What we call history is merely the thread that happened to hold — and we mistake the thread for the loom.

The universe is not required to be in perfect harmony with human ambition. It is indifferent to our need for certainty, and it is precisely this indifference that makes the pursuit of understanding so urgent.

The universe is under no obligation to make sense to you.

It is the mark of an educated mind to be able to entertain a thought without accepting it.

It is not the answer that enlightens, but the question. Déceler, c'est créer. To detect is to create.

It is not when truth is dirty, but when it is shallow, that the lover of knowledge is reluctant to wade into its waters.

The peculiarity of the evidence of mathematics is that all the argument is on one side. There are no objections, and no answers to objections. But on every subject on which difference of opinion is possible, the truth depends on a balance of two sets of reasons.

The longing to behold this pre-established harmony is the source of the inexhaustible patience with which Spinoza must have waited for years to see his cherished conception of a mathematical proof of the existence of God.

A fact acquires its true and full value only through the idea which is developed from it.

It is a truth very certain that, when it is not in our power to determine what is true, we ought to follow what is most probable; and even if we cannot discover which of the alternatives is the more probable, we must nevertheless choose one of them.

We know accurately only when we know little; with knowledge doubt increases.

We are apt to think that our ideas are a measure of things; but they are only a measure of ourselves.

It is not the answer that enlightens, but the question. Decadence begins when questions are suppressed and we are left only with the comfort of old replies.

The historian must not try to know what is truth, if he values his honesty; for, if he cares for his truths, he is certain to falsify his facts.

We are all capable of believing things which we know to be untrue, and then, when we are finally proved wrong, impudently twisting the facts so as to show that we were right. Intellectually, it is possible to carry on this process for an indefinite time: the only check on it is that sooner or later a false belief bumps up against solid reality, usually on a battlefield.

The greatest obstacle to discovery is not ignorance — it is the illusion of knowledge.

The most thought-provoking thing in our thought-provoking time is that we are still not thinking.

The observer, when he seems to himself to be observing a stone, is really, if physics is to be believed, observing the effects of the stone upon himself.

The naturalist hardly expects to be believed when he relates the instincts of animals; yet the physiologist is compelled to believe them, because he cannot explain them away.

The demand of the human intellect is for a world in which something is permanently true. Science gives us a world in which everything is provisionally true — which is not at all the same thing.

We are reluctant to believe that the world we see is not the whole world. Yet the history of knowledge is largely the history of such reluctance being overcome.

We are apt to think that our ideas are the spontaneous product of the mind working upon experience; but in truth our ideas are largely the inheritance of past thought, and the experience upon which they work is itself colored by inherited assumptions.

The truth is that we never know for certain about anything. The degree of assurance we feel about any proposition is not a measure of its truth, but a measure of our familiarity with the evidence bearing on it.

It is a test of true theories not only to account for but to predict phenomena. We ought to accept a theory if it predicts things which observation subsequently confirms, and if no rival theory is equally successful.

We are compelled to feel that the world presented to our senses is not the world as it really is, but only the world as it appears to beings constituted as we are. The thing in itself remains forever unknowable.

It is not what the man of science believes that distinguishes him, but how and why he believes it. His beliefs are tentative, not dogmatic; they are based on evidence, not on authority or intuition.

The universe is under no obligation to make sense to you. But stranger still is the fact that it does — partially, provisionally, and always at the cost of uprooting what we thought we already knew.

The fact that an opinion has been widely held is no evidence whatever that it is not utterly absurd; indeed in view of the silliness of the majority of mankind, a widespread belief is more likely to be foolish than sensible.

A new scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die, and a new generation grows up that is familiar with it.

The mind is furnished with a set of instincts which seek out certain kinds of phenomena and ask for explanations of certain kinds of things. Any answer to a question which does not ask or explain the right kind of thing will be philosophically frustrated and dull.

The mind has not merely made a discovery of external fact; it has altered its own character by the attempt to know external fact.

The notion that science and spirituality are forever at war is the invention of twits who understand neither.

The human mind is like a flashlight in the dark. It illuminates a small circle of the world around us, but beyond that circle lies an infinite darkness that we can never fully penetrate.

The opposite of a correct statement is a false statement. But the opposite of a profound truth may well be another profound truth.

To know the world one must construct it. One does not go for a walk in order to walk but to construct the world at each step.

The principle of parsimony suggests that entities should not be multiplied beyond necessity; yet in the study of human nature, we continually discover that the simple explanation was merely the one we had grown comfortable defending.

The mind has shown itself capable of grasping the incomprehensible; it has stood in the presence of the infinite and perceived it as finite; it has measured the unmeasurable and found dimensions.

We do not think in words alone. We think in images, in sensations, in the movement and flow of muscle and nerve. Yet we must clothe our thought in words to communicate it, and so our words always betray the living truth a little.

The true nature of things is in their particulars, not in generalities; we know a thing by knowing its individual characteristics, not by subsumming it under a class.

The metaphor of the library is the metaphor of the world. We search for the infinite in the finite, and we find it nowhere but in language itself.

The true nature of things is in their particulars, not in generalities; we know the world through its infinite variations, not through abstract rules that pretend to govern them.