Claude Bernard Quotations

The experimenter who does not know what he is looking for will not understand what he finds.

It is what we know already that often prevents us from learning.

Observation is a passive science, experimentation an active science.

Man can learn nothing except by going from the known to the unknown.

Put off your imagination, as you put off your overcoat, when you enter the laboratory. Put it on again, as you put on your overcoat, when you leave.

In teaching man, experimental science results in lessening his pride more and more by proving to him every day that primary causes, like the objective reality of things, will be hidden from him forever and that he can only know relations.

A fact in itself is nothing. It is valuable only for the idea attached to it, or for the proof which it furnishes.

The true worth of an experimenter consists in his pursuing not only what he seeks in his experiment, but also what he did not seek.

The investigator should have a robust faith - and yet not believe.

Mediocre men often have the most acquired knowledge

To be worthy of the name, an experimenter must be at once theorist and practitioner. While he must completely master the art of establishing experimental facts, which are the materials of science, he must also clearly understand the scientific principles which guide his reasoning through the varied experimental study of natural phenomena. We cannot separate these two things: head and hand. An able hand, without a head to direct it, is a blind tool; the head is powerless without its executive hand.

Laplace considers astronomy a science of observation, because we can only observe the movements of the planets; we cannot reach them, indeed, to alter their course and to experiment with them. "On earth," said Laplace, "we make phenomena vary by experiments; in the sky, we carefully define all the phenomena presented to us by celestial motion." Certain physicians call medicine a science of observations, because they wrongly think that experimentation is inapplicable to it.

The goal of scientific physicians in their own science ... is to reduce the indeterminate. Statistics therefore apply only to cases in which the cause of the facts observed is still indeterminate.

A man of science rises ever, in seeking truth; and if he never finds it in its wholeness, he discovers nevertheless very significant fragments; and these fragments of universal truth are precisely what constitutes science.

Theories are like a stairway; by climbing, science widens its horizon more and more, because theories embody and necessarily include proportionately more facts as they advance.

Well-observed facts, though brought to light by passing theories, will never die; they are the material on which alone the house of science will at last be built.

When a physician is called to a patient, he should decide on the diagnosis, then the prognosis, and then the treatment. ... Physicians must know the evolution of the disease, its duration and gravity in order to predict its course and outcome. Here statistics intervene to guide physicians, by teaching them the proportion of mortal cases, and if observation has also shown that the successful and unsuccessful cases can be recognized by certain signs, then the prognosis is more certain.

Ardent desire for knowledge, in fact, is the one motive attracting and supporting investigators in their efforts; and just this knowledge, really grasped and yet always flying before them, becomes at once their sole torment and their sole happiness. Those who do not know the torment of the unknown cannot have the joy of discovery which is certainly the liveliest that the mind of man can ever feel.

As soon as the circumstances of an experiment are well known, we stop gathering statistics. ... The effect will occur always without exception, because the cause of the phenomena is accurately defined. Only when a phenomenon includes conditions as yet undefined,Only when a phenomenon includes conditions as yet undefined, can we compile statistics. ... we must learn therefore that we compile statistics only when we cannot possibly help it; for in my opinion, statistics can never yield scientific truth.

Mediocre men often have the most acquired knowledge. It is in the darker. It is in the darker regions of science that great men are recognized; they are marked by ideas which light up phenomena hitherto obscure and carry science forward.

We must keep our freedom of mind, ... and must believe that in nature what is absurd, according to our theories, is not always impossible.

It has often been said that, to make discoveries, one must be ignorant. This opinion, mistaken in itself, nevertheless conceals a truth. It means that it is better to know nothing than to keep in mind fixed ideas based on theories whose confirmation we constantly seek, neglecting meanwhile everything that fails to agree with them.

When we meet a fact which contradicts a prevailing theory, we must accept the fact and abandon the theory, even when the theory is supported by great names and generally accepted.

Effects vary with the conditions which bring them to pass, but laws do not vary. Physiological and pathological states are ruled by the same forces; they differ only because of the special conditions under which the vital laws manifest themselves.

The fact that knowledge endlessly recedes as the investigator is about to grasp it is what constitutes at the same time his torment and happiness.

Feeling alone guides the mind.

Our ideas are only intellectual instruments which we use to break into phenomena; we must change them when they have served their purpose, as we change a blunt lancet that we have used long enough.

The science of life is a superb and dazzlingly lighted hall which may be reached only by passing through a long and ghastly kitchen.

The stability of the internal medium is a primary condition for the freedom and independence of certain living bodies in relation to the environment surrounding them.

The physiologist is not a man of the world, he is a scientist, a man caught and absorbed by a scientific idea that he pursues; he no longer hears the cries of the animals, no longer sees the flowing blood, he sees only his idea: organisms that hide from him problems that he wants to discover. He doesn't feel that he is in a horrible carnage; under the influence of a scientific idea, he pursues with delight a nervous filament inside stinking and livid flesh that for any other person would be an object of disgust and horror.

In every enterprise ... the mind is always reasoning, and, even when we seem to act without a motive, an instinctive logic still directs the mind. Only we are not aware of it, because we begin by reasoning before we know or say that we are reasoning, just as we begin by speaking before we observe that we are speaking, and just as we begin by seeing and hearing before we know what we see or what we hear.

Real science exists, then, only from the moment when a phenomenon is accurately defined as to its nature and rigorously determined in relation to its material conditions, that is, when its law is known. Before that, we have only groping and empiricism.

In these researches I followed the principles of the experimental method that we have established, i.e., that, in presence of a well-noted, new fact which contradicts a theory, instead of keeping the theory and abandoning the fact, I should keep and study the fact, and I hastened to give up the theory.

A discovery is generally an unforeseen relation not included in theory.

When entering on new ground we must not be afraid to express even risky ideas so as to stimulate research in all directions. As Priestley put it, we must not remain inactive through false modesty based on fear of being mistaken.

With the aid of these active experimental sciences man becomes an inventor of phenomena, a real foreman of creation; and under this head we cannot set limits to the power that he may gain over nature through future progress of the experimental sciences.

Science rejects the indeterminate.

Particular facts are never scientific; only generalization can establish science.

Science admits no exceptions; otherwise there would be no determinism in science, or rather, there would be no science.

All the vital mechanisms, varied as they are, have only one object, that of preserving constant the conditions of life in the internal environment.

The mental never influences the physical. It is always the physical that modifies the mental, and when we think that the mind is diseased, it is always an illusion.

A great discovery is a fact whose appearance in science gives rise to shining ideas, whose light dispels many obscurities and shows us new paths.

The eloquence of a scientist is clarity; scientific truth is always more luminous when its beauty is unadorned than when it is tricked out in the embellishments with which our imagination would seek to clothe it.

But while I accept specialization in the practice, I reject it utterly in the theory of science.

Experiment is fundamentally only induced observation.

The better educated we are and the more acquired information we have, the better prepared shall we find our minds for making great and fruitful discoveries.

In science, the best precept is to alter and exchange our ideas as fast as science moves ahead.

The constancy of the internal environment is the condition for free and independent life: the mechanism that makes it possible is that which assured the maintenance, with the internal environment, of all the conditions necessary for the life of the elements.

If I had to define life in a single phrase, I should clearly express my thought of throwing into relief one characteristic which, in my opinion, sharply differentiates biological science. I should say: life is creation.

First causes are outside the realm of science.

In a word, I consider hospitals only as the entrance to scientific medicine; they are the first field of observation which a physician enters; but the true sanctuary of medical science is a laboratory; only there can he seek explanations of life in the normal and pathological states by means of experimental analysis.

A contemporary poet has characterized this sense of the personality of art and of the impersonality of science in these words,-'Art is myself; science is ourselves. '

[Those] who have an excessive faith in their theories or in their ideas are not only poorly disposed to make discoveries, but they also make very poor observations.

The joy of discovery is certainly the liveliest that the mind of man can ever feel.

In the philosophic sense, observation shows and experiment teaches.

Man does not limit himself to seeing; he thinks and insists on learning the meaning of phenomena whose existence has been revealed to him by observation. So he reasons, compares facts, puts questions to them, and by the answers which he extracts, tests one by another. This sort of control, by means of reasoning and facts, is what constitutes experiment, properly speaking; and it is the only process that we have for teaching ourselves about the nature of things outside us.

Obervation is a passive science, experimentation is an active science.

We must never make experiments to confirm our ideas, but simply to control them.

It is impossible to devise an experiment without a preconceived idea; devising an experiment, we said, is putting a question; we never conceive a question without an idea which invites an answer. I consider it, therefore, an absolute principle that experiments must always be devised in view of a preconceived idea, no matter if the idea be not very clear nor very well defined.

Even mistaken hypotheses and theories are of use in leading to discoveries. This remark is true in all the sciences. The alchemists founded chemistry by pursuing chimerical problems and theories which are false. In physical science, which is more advanced than biology, we might still cite men of science who make great discoveries by relying on false theories. It seems, indeed, a necessary weakness of our mind to be able to reach truth only across a multitude of errors and obstacles.

Now, a living organism is nothing but a wonderful machine endowed with the most marvellous properties and set going by means of the most complex and delicate mechanism.

The first entirely vital action, so termed because it is not effected outside the influence of life, consists in the creation of the glycogenic material in the living hepatic tissue. The second entirely chemical action, which can be effected outside the influence of life, consists in the transformation of the glycogenic material into sugar by means of a ferment.

We achieve more than we know. We know more than we understand. We understand more than we can explain.

Science does not permit exceptions.

Priestley [said] that each discovery we make shows us many others that should be made.

I do not ... reject the use of statistics in medicine, but I condemn not trying to get beyond them and believing in statistics as the foundation of medical science. ... Statistics ... apply only to cases in which the cause of the facts observed is still [uncertain or] indeterminate. ... There will always be some indeterminism ... in all the sciences, and more in medicine than in any other. But man's intellectual conquest consists in lessening and driving back indeterminism in proportion as he gains ground for determinism by the help of the experimental method..

Men who have excessive faith in their theories ... make poor observations, because they choose among the results of their experiments only what suits their object, neglecting whatever is unrelated to it and carefully setting aside everything which might tend toward the idea they wish to combat

Il ne fallait jamais faire des expériences pour confirmer ses idées, mais simplement pour les contrôler. We must never make experiments to confirm our ideas, but simply to control them.

The first requirement in using statistics is that the facts treated shall be reduced to comparable units.

In the patient who succumbed, the cause of death was evidently something which was not found in the patient who recovered; this something we must determine, and then we can act on the phenomena or recognize and foresee them accurately. But not by statistics shall we succeed in this; never have statistics taught anything, and never can they teach anything about the nature of the phenomenon.

Proof that a given condition always precedes or accompanies a phenomenon does not warrant concluding with certainty that a given condition is the immediate cause of that phenomenon. It must still be established that when this condition is removed, the phenomen will no longer appear.

The minds that rise and become really great are never self-satisfied, but still continue to strive.

Progress is achieved by exchanging our theories for new ones which go further than the old, until we find one based on a larger number of facts. ... Theories are only hypotheses, verified by more or less numerous facts. Those verified by the most facts are the best, but even then they are never final, never to be absolutely believed.

The great experimental principle, then, is doubt, that philosophic doubt which leaves to the mind its freedom and initiative, and from which the virtues most valuable to investigators in physiology and medicine are derived.

Tout est poison, rien n'est poison, tout est une question de dose. Everything is poisonous, nothing is poisonous, it is all a matter of dose.

We must remain, in a word, in an intellectual disposition which seems paradoxical, but which, in my opinion, represents the true mind of the investigator. We must have a robust faith and yet not believe.

True science teaches us to doubt and, in ignorance, to refrain.

Descriptive anatomy is to physiology what geography is to history, and just as it is not enough to know the typography of a country to understand its history, so also it is not enough to know the anatomy of organs to understand their functions.

Hatred is the most clear- sighted, next to genius....

The terrain is everything; the germ is nothing,

The doubter is a true man of science: he doubts only himself and his interpretations, but he believes in science.

Art is 'I'; science is 'we'.

We must alter theory to adapt it to nature, but not nature to adapt it to theory.‎

Men who believe too firmly in their theories, do not believe enough in the theories of others. So ... these despisers of their fellows ... make experiments only to destroy a theory, instead of to seek the truth.

Man can learn nothing unless he proceeds from the known to the unknown.

Those who do not know the torment of the unknown cannot have the joy of discovery.

Science increases our power in proportion as it lowers our pride.

Men who have excessive faith in their theories or ideas are not only ill prepared for making discoveries; they also make very poor observations. Of necessity, they observe with a preconceived idea, and when they devise an experiment, they can see, in its results,only a confirmation of their theory. In this way they distort observation and often neglect very important facts because they do not further their aim.