Henri Poincare

A sane mind should not be guilty of a logical fallacy, yet there are very fine minds incapable of following mathematical demonstrations.

It is the harmony of the diverse parts, their symmetry, their happy balance; in a word it is all that introduces order, all that gives unity, that permits us to see clearly and to comprehend at once both the ensemble and the details.

If that enabled us to predict the succeeding situation with the same approximation, that is all we require, and we should say that the phenomenon had been predicted, that it is governed by the laws.

A small error in the former will produce an enormous error in the latter.

Science is facts.

If one looks at the different problems of the integral calculus which arise naturally when one wishes to go deep into the different parts of physics, it is impossible not to be struck by the analogies existing.

Invention consists in avoiding the constructing of useless contraptions and in constructing the useful combinations which are in infinite minority.

Geometry is not true, it is advantageous.

What is it indeed that gives us the feeling of elegance in a solution, in a demonstration?

A very small cause which escapes our notice determines a considerable effect that we cannot fail to see, and then we say that the effect is due to chance.

It is far better to foresee even without certainty than not to foresee at all.

It has adopted the geometry most advantageous to the species or, in other words, the most convenient.

Thought is only a flash between two long nights, but this flash is everything.

The mathematical facts worthy of being studied are those which, by their analogy with other facts, are capable of leading us to the knowledge of a physical law.

No more than these machines need the mathematician know what he does.

Mathematicians do not study objects, but relations between objects.

Just as houses are made of stones, so is science made of facts.

In the old days when people invented a new function they had something useful in mind.

Facts do not speak.

Absolute space, that is to say, the mark to which it would be necessary to refer the earth to know whether it really moves, has no objective existence.

Hypotheses are what we lack the least.

Point set topology is a disease from which the human race will soon recover.

Science is built up of facts, as a house is with stones. But a collection of facts is no more a science than a heap of stones is a house.

One would have to have completely forgotten the history of science so as to not remember that the desire to know nature has had the most constant and the happiest influence on the development of mathematics.

To invent is to discern, to choose.

How is an error possible in mathematics?

The scientist does not study nature because it is useful; he studies it because he delights in it, and he delights in it because it is beautiful.

A scientist worthy of his name, about all a mathematician, experiences in his work the same impression as an artist; his pleasure is as great and of the same nature.

Need we add that mathematicians themselves are not infallible?

Mathematics is the art of giving the same name to different things.

Thus, they are free to replace some objects by others so long as the relations remain unchanged.

Ideas rose in clouds; I felt them collide until pairs interlocked, so to speak, making a stable combination.

If nature were not beautiful, it would not be worth knowing, and if nature were not worth knowing, life would not be worth living.

It is through science that we prove, but through intuition that we discover.

Mathematicians are born, not made.

If we knew exactly the laws of nature and the situation of the universe at the initial moment, we could predict exactly the situation of the same universe at a succeeding moment.

The mind uses its faculty for creativity only when experience forces it to do so.

Mathematical discoveries, small or great are never born of spontaneous generation.

To doubt everything, or, to believe everything, are two equally convenient solutions; both dispense with the necessity of reflection.