Henri Poincare Quotes & Sayings

Often when works at a hard question, nothing good is accomplished at the first attack. Then one takes a rest, long or short, and sits down anew to the work. During the first half-hour, as before, nothing is found, and then all of a sudden the decisive idea presents itself to the mind. — Henri Poincare

It is by logic we prove. It is by intuition we discover. — Henri Poincare

For a long time the objects that mathematicians dealt with were mostly ill-defined; one believed one knew them, but one represented them with the senses and imagination; but one had but a rough picture and not a precise idea on which reasoning could take hold. — Henri Poincare

Intuition is more important to discovery than logic. — Henri Poincare

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 Poincare

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

Science is facts. — Henri Poincare

Physicists believe that the Gaussian law has been proved in mathematics while mathematicians think that it was experimentally established in physics. — Henri Poincare

When the logician has resolved each demonstration into a host of elementary operations, all of them correct, he will not yet be in possession of the whole reality, that indefinable something that constitutes the unity ... Now pure logic cannot give us this view of the whole; it is to intuition that we must look for it. — Henri Poincare

Every phenomenon, however trifling it be, has a cause, and a mind infinitely powerful, and infinitely well-informed concerning the laws of nature could have foreseen it from the beginning of the ages. If a being with such a mind existed, we could play no game of chance with him; we should always lose. — Henri Poincare

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. — Henri Poincare

The feeling of mathematical beauty, of the harmony of numbers and of forms, of geometric elegance. It is a genuinely aesthetic feeling, which all mathematicians know — Henri Poincare

Pure logic could never lead us to anything but tautologies; it can create nothing new; not from it alone can any science issue. — Henri Poincare

All of mathematics is a tale about groups. — Henri Poincare

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

It is not order only, but unexpected order, that has value. — Henri Poincare

What is a good definition? For the philosopher or the scientist, it is a definition which applies to all the objects to be defined, and applies only to them; it is that which satisfies the rules of logic. But in education it is not that; it is one that can be understood by the pupils. — Henri Poincare

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

Zero is the number of objects that satisfy a condition that is never
satisfied. But as never means "in no case", I do not see that any progress has been made. — Henri Poincare

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. — Henri Poincare

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

This harmony that human intelligence believes it discovers in nature - does it exist apart from that intelligence? No, without doubt, a reality completely independent of the spirit which conceives it, sees it or feels it, is an impossibility. A world so exterior as that, even if it existed, would be forever inaccessible to us. But what we call objective reality is, in the last analysis, that which is common to several thinking beings, and could be common to all; this common part, we will see, can be nothing but the harmony expressed by mathematical laws. — Henri Poincare

So is not mathematical analysis then not just a vain game of the mind? To the physicist it can only give a convenient language; but isn't that a mediocre service, which after all we could have done without; and, it is not even to be feared that this artificial language be a veil, interposed between reality and the physicist's eye? Far from that, without this language most of the initimate analogies of things would forever have remained unknown to us; and we would never have had knowledge of the internal harmony of the world, which is, as we shall see, the only true objective reality. — Henri Poincare

It is a misfortune for a science to be born too late when the means of observation have become too perfect. That is what is happening at this moment with respect to physical chemistry; the founders are hampered in their general grasp by third and fourth decimal places. — Henri Poincare

A first fact should surprise us, or rather would surprise us if we were not used to it. How does it happen there are people who do not understand mathematics? If mathematics invokes only the rules of logic, such as are accepted by all normal minds ... how does it come about that so many persons are here refractory? — Henri Poincare

A cat is witty, he has nerve, he knows how to do precisely the right thing at the right moment. — Henri Poincare

Most striking at first is the appearance of sudden illumination, a manifest sign of long unconscious prior work. — Henri Poincare

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

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. — Henri Poincare

Logic sometimes makes monsters. For half a century we have seen a mass of bizarre functions which appear to be forced to resemble as little as possible honest functions which serve some purpose. — Henri Poincare

The aim of Mathematical Physics is not only to facilitate for the physicist the numerical calculation of certain constants or the integration of certain differential equations. It is besides, it is above all, to reveal to him the hidden harmony of things in making him see them in a new way. — Henri Poincare

To invent is to discern, to choose. — Henri Poincare

Doubt everything or believe everything: these are two equally convenient strategies. With either we dispense with the need for reflection. — Henri Poincare

Is is by logic that we prove, but by intuition that we discover. — Henri Poincare

I then began to study arithmetical questions without any great apparent result, and without suspecting that they could have the least connexion with my previous researches. Disgusted at my want of success, I went away to spend a few days at the seaside, and thought of entirely different things. One day, as I was walking on the cliff, the idea came to me, again with the same characteristics of conciseness, suddenness, and immediate certainty, that arithmetical transformations of indefinite ternary quadratic forms are identical with those of non-Euclidian geometry. — Henri Poincare

Every good mathematician should also be a good chess player and vice versa. — Henri Poincare

It is often said that experiments should be made without preconceived ideas. That is impossible. Not only would it make every experiment fruitless, but even if we wished to do so, it could not be done. Every man has his own conception of the world, and this he cannot so easily lay aside. We must, example, use language, and our language is necessarily steeped in preconceived ideas. Only they are unconscious preconceived ideas, which are a thousand times the most dangerous of all. — Henri Poincare

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

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. — Henri Poincare

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

There are no solved problems; there are only problems that are more or less solved. — Henri Poincare

Pure analysis puts at our disposal a multitude of procedures whose infallibility it guarantees; it opens to us a thousand different ways on which we can embark in all confidence; we are assured of meeting there no obstacles; but of all these ways, which will lead us most promptly to our goal? Who shall tell us which to choose? We need a faculty which makes us see the end from afar, and intuition is this faculty. It is necessary to the explorer for choosing his route; it is not less so to the one following his trail who wants to know why he chose it. — Henri Poincare

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. — Henri Poincare

Talk with M. Hermite. He never evokes a concrete image, yet you soon perceive that the more abstract entities are to him like living creatures. — Henri Poincare

The advance of science is not comparable to the changes of a city, where old edifices are pitilessly torn down to give place to new, but to the continuous evolution of zoologic types which develop ceaselessly and end by becoming unrecognisable to the common sight, but where an expert eye finds always traces of the prior work of the centuries past. One must not think then that the old-fashioned theories have been sterile and vain. — Henri Poincare

Sociology is the science with the greatest number of methods and the least results. — Henri Poincare

Mathematicians do not deal in objects, but in relations between objects; thus, they are free to replace some objects by others so lone as the relations remain unchanged. Content to them is irrelevant; they are interested in form only. — Henri Poincare

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

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

It is impossible to study the works of the great mathematicians, or even those of the lesser, without noticing and distinguishing two opposite tendencies, or rather two entirely different kinds of minds. The one sort are above all preoccupied with logic; to read their works, one is tempted to believe they have advanced only step by step, after the manner of a Vauban who pushes on his trenches against the place besieged, leaving nothing to chance. The other sort are guided by intuition and at the first stroke make quick but sometimes precarious conquests, like bold cavalrymen of the advance guard.
[1913, p210] — Henri Poincare

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

The Scientist must set in order. Science is built up with 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. — Henri Poincare

But for harmony beautiful to contemplate, science would not be worth following. — Henri Poincare

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

A very small cause, which escapes us, determines a considerable effect which we cannot ignore, and we say that this effect is due to chance. — Henri Poincare

All that we can hope from these inspirations, which are the fruits of unconscious work, is to obtain points of departure for such calculations. As for the calculations themselves, they must be made in the second period of conscious work which follows the inspiration, and in which the results of the inspiration are verified and the consequences deduced. — Henri Poincare

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

When the physicists ask us for the solution of a problem, it is not drudgery that they impose on us, on the contrary, it is us who owe them thanks. — Henri Poincare

Later generations will regard Mengenlehre (set theory) as a disease from which one has recovered. — Henri Poincare

All great progress takes place when two sciences come together, and when their resemblance proclaims itself, despite the apparent disparity of their substance. — Henri Poincare

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

The task of the educator is to make the child's spirit pass again where its forefathers have gone, moving rapidly through certain stages but suppressing none of them. In this regard, the history of science must be our guide. — Henri Poincare

Thought must never submit, neither to a dogma, nor to a party, nor to a passion, nor to an interest, nor to a preconceived idea, nor to whatever it may be, save to the facts themselves, because, for thought, submission would mean ceasing to be. — Henri Poincare

Facts do not speak. — Henri Poincare

It may happen that small differences in the initial conditions produce very great ones in the final phenomena. — Henri Poincare

Einstein does not remain attached to the classical principles, and when presented with a problem in physics he quickly envisages all of its possibilities. This leads immediately in his mind to the prediction of new phenomena which may one day be verified by experiment. — Henri Poincare

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. — Henri Poincare

Hypotheses are what we lack the least. — Henri Poincare

If we ought not to fear mortal truth, still less should we dread scientific truth. In the first place it can not conflict with ethics? But if science is feared, it is above all because it can give no happiness? Man, then, can not be happy through science but today he can much less be happy without it. — Henri Poincare

But all of my efforts served only to make me better acquainted with the difficulty, which in itself was something. — Henri Poincare

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. — Henri Poincare

Tolstoi explains somewhere in his writings why, in his opinion, "Science for Science's sake" is an absurd conception. We cannot know all the facts since they are infinite in number. We must make a selection ... guided by utility ... Have we not some better occupation than counting the number of lady-birds in existence on this planet? — Henri Poincare

Geometry is the art of correct reasoning from incorrectly drawn figures. — Henri Poincare

Need we add that mathematicians themselves are not infallible? — Henri Poincare

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

Doubting everything and believing everything are two equally convenient solutions that guard us from having to think — Henri Poincare

It is by logic that we prove, but by intuition that we discover. To know how to criticize is good, to know how to create is better. — Henri Poincare

All that is not thought is pure nothingness; since we can think only thoughts, and all the words we use to speak of things can express only thoughts, to say there is something other than thought is therefore an affirmation which can have no meaning. — Henri Poincare

Analyse data just so far as to obtain simplicity and no further. — Henri Poincare

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

How is it that there are so many minds that are incapable of understanding mathematics? ... the skeleton of our understanding, ... and actually they are the majority ... We have here a problem that is not easy of solution, but yet must engage the attention of all who wish to devote themselves to education. — Henri Poincare

I left Caen, where I was living, to go on a geological excursion under the auspices of the School of Mines. The incidents of the travel made me forget my mathematical work. Having reached Coutances, we entered an omnibus to go to some place or other. At the moment when I put my foot on the step, the idea came to me, without anything in my former thoughts seeming to have paved the way for it, that the transformations I had used to define the Fuchsian functions were identical with those of non-Euclidean geometry. I did not verify the idea; I should not have had time, as upon taking my seat in the omnibus, I went on with a conversation already commenced, but I felt a perfect certainty. On my return to Caen, for convenience sake, I verified the result at my leisure. — Henri Poincare

Consider now the Milky Way. Here also we see an innumerable dust, only the grains of this dust are no longer atoms but stars; these grains also move with great velocities, they act at a distance one upon another, but this action is so slight at great distances that their trajectories are rectilineal; nevertheless, from time to time, two of them may come near enough together to be deviated from their course, like a comet that passed too close to Jupiter. In a word, in the eyes of a giant, to whom our Suns were what our atoms are to us, the Milky Way would only look like a bubble of gas. — Henri Poincare

I entered an omnibus to go to some place or other. At that moment when I put my foot on the step the idea came to me, without anything in my former thoughts seeming to have paved the way for it, that the transformations I had used to define the Fuchsian functions were identical with non-Euclidean geometry. — Henri Poincare

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 Poincare

Mathematicians are born, not made. — Henri Poincare

Why is it that showers and even storms seem to come by chance, so that many people think it quite natural to pray for rain or fine weather, though they would consider it ridiculous to ask for an eclipse by prayer? — Henri Poincare

Thus, be it understood, to demonstrate a theorem, it is neither necessary nor even advantageous to know what it means ... — Henri Poincare

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

How is an error possible in mathematics? — Henri Poincare

The aim of science is not things themselves, as the dogmatists in their simplicity imagine, but the relation between things. — Henri Poincare

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

To doubt everything and to believe everything are two equally convenient solutions; each saves us from thinking. — Henri Poincare

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

All the scientist creates in a fact is the language in which he enunciates it. If he predicts a fact, he will employ this language, and for all those who can speak and understand it, his prediction is free from ambiguity. Moreover, this prediction once made, it evidently does not depend upon him whether it is fulfilled or not. — Henri Poincare

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

Mathematicians do not study objects, but relations between objects. — Henri Poincare

Astronomy is useful because it raises us above ourselves; it is useful because it is grand; ... It shows us how small is man's body, how great his mind, since his intelligence can embrace the whole of this dazzling immensity, where his body is only an obscure point, and enjoy its silent harmony. — Henri Poincare

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

If we wish to foresee the future of mathematics, our proper course is to study the history and present condition of the science. — Henri Poincare