Henri Poincaré quotes - page 2

Henri Poincaré was a French mathematician, theoretical physicist, and philosopher of science. Considered one of the last universalists, his work laid the foundations for chaos theory and modern topology. He made significant contributions to mathematical physics, celestial mechanics, and the philosophy of mathematics. Here are 104 of his quotes:

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.

Henri Poincaré

Hypotheses are what we lack the least.

Henri Poincaré

Geometry is not true, it is advantageous.

Henri Poincaré

How is an error possible in mathematics?

Henri Poincaré

Mathematicians do not study objects, but relations between objects.

Henri Poincaré

It is the simple hypotheses of which one must be most wary; because these are the ones that have the most chances of passing unnoticed.

Henri Poincaré

... treatises on mechanics do not clearly distinguish between what is experiment, what is mathematical reasoning, what is convention, and what is hypothesis.

Henri Poincaré

As we can not give a general definition of energy, the principle of the conservation of energy signifies simply that there is something which remains constant.

Henri Poincaré

Now what is science? ...it is before all a classification, a manner of bringing together facts which appearances separate, though they are bound together by some natural and hidden kinship. Science, in other words, is a system of relations. ...it is in relations alone that objectivity must be sought. ...it is relations alone which can be regarded as objective. External objects... are really objects and not fleeting and fugitive appearances, because they are not only groups of sensations, but groups cemented by a constant bond. It is this bond, and this bond alone, which is the object in itself, and this bond is a relation.

Henri Poincaré

Experiment is the sole source of truth. It alone can teach us something new; it alone can give us certainty.

Henri Poincaré

Chance ... must be something more than the name we give to our ignorance.

Henri Poincaré

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

Henri Poincaré

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

Henri Poincaré

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

Henri Poincaré

For an aggregate of sensations to have become a remembrance capable of classification in time, it must have ceased to be actual, we must have lost the sense of its infinite complexity, otherwise it would have remained present. It must, so to speak, have crystallized around a center of associations of ideas which will be a sort of label. It is only when they have lost all life that we can classify our memories in time as a botanist arranges dried flowers in his herbarium.

Henri Poincaré

Is the position tenable, that certain phenomena, possible in Euclidean space, would be impossible in non-Euclidean space, so that experience, in establishing these phenomena, would directly contradict the non-Euclidean hypothesis? For my part I think no such question can be put. To my mind it is precisely equivalent to the following, whose absurdity is patent to all eyes: are there lengths expressible in meters and centimeters, but which can not be measured in fathoms, feet, and inches, so that experience, in ascertaining the existence of these lengths, would directly contradict the hypothesis that there are fathoms divided into six feet?

Henri Poincaré

If, then, a phenomenon admits of a complete mechanical explanation, it will admit of an infinity of others, that will render an account equally well of all the particulars revealed by experiment.

Henri Poincaré

Mathematics have a triple aim. They must furnish an instrument for the study of nature. But that is not all: they have a philosophic aim and, I dare maintain, an esthetic aim. They must aid the philosopher to fathom the notions of number, of space, of time. And above all, their adepts find therein delights analogous to those given by painting and music. They admire the delicate harmony of numbers and forms; they marvel when a new discovery opens to them an unexpected perspective; and has not the joy they thus feel the esthetic character, even though the senses take no part therein? Only a privileged few are called to enjoy it fully, it is true, but is not this the case for all the noblest arts? This is why I do not hesitate to say that mathematics deserve to be cultivated for their own sake, and the theories inapplicable to physics as well as the others. Even if the physical aim and the esthetic aim were not united, we ought not to sacrifice either.

Henri Poincaré

If we study the history of science we see happen two inverse phenomena... Sometimes simplicity hides under complex appearances; sometimes it is the simplicity which is apparent, and which disguises extremely complicated realities. ...No doubt, if our means of investigation should become more and more penetrating, we should discover the simple under the complex, then the complex under the simple, then again the simple under the complex, and so on, without our being able to foresee what will be the last term. We must stop somewhere, and that science may be possible, we must stop when we have found simplicity. This is the only ground on which we can rear the edifice of our generalizations.

Henri Poincaré

There is no science apart from the general. It may even be said that the very object of the exact sciences is to spare us these direct verifications.

Henri Poincaré

Logic teaches us that on such and such a road we are sure of not meeting an obstacle; it does not tell us which is the road that leads to the desired end. For this, it is necessary to see the end from afar, and the faculty which teaches us to see is intuition. Without it, the geometrician would be like a writer well up in grammar but destitute of ideas.

Henri Poincaré

Does the harmony the human intelligence thinks it discovers in nature exist outside of this intelligence? No, beyond doubt, a reality completely independent of the mind which conceives it, sees or feels it, is an impossibility.

Henri Poincaré