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Claude Bernard

(12 Jul 1813 - 10 Feb 1878)

French physiologist who helped establish the principles of experimentation in the life sciences. His Introduction to the Study of Experimental Medicine (1865) is a scientific classic.

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La théorie est l’hypothèse vérifiée, après qu’elle a été soumise au contrôle du raisonnement et de la critique expérimentale. La meilleure théorie est celle qui a été vérifiée par le plus grand nombre de faits. Mais une théorie, pour rester bonne, doit toujours se modifier avec les progrès de la science et demeurer constamment soumise à la vérification et à la critique des faits nouveaux qui apparaissent.
A theory is a verified hypothesis, after it has been submitted to the control of reason and experimental criticism. The soundest theory is one that has been verified by the greatest number of facts. But to remain valid, a theory must be continually altered to keep pace with the progress of science and must be constantly resubmitted to verification and criticism as new facts appear.

— Claude Bernard

Original work in French, Introduction à l'Étude de la Médecine Expérimentale (1865), 385. English translation by Henry Copley Green in An Introduction to the Study of Experimental Medicine (1927, 1957), 220.

La théorie n’est que l’idée scientifique contrôlée par l’expérience.
A theory is merely a scientific idea controlled by experiment.

— Claude Bernard

Original work in French, Introduction à l'Étude de la Médecine Expérimentale (1865), 40. English translation by Henry Copley Green in An Introduction to the Study of Experimental Medicine (1927, 1957), 26.

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

— Claude Bernard

From An Introduction to the Study of Experimental Medicine (1865), as translated by Henry Copley Greene (1957), 38.

Science quotes on: | Discovery (837) | Relation (166) | Theory (1015) | Unforeseen (11)

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

— Claude Bernard

From An Introduction to the Study of Experimental Medicine (1865), as translated by Henry Copley Greene (1957), 25.

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.

— Claude Bernard

An Introduction to the Study of Experimental Medicine (1865, translation 1927, 1957), 170.

If an idea presents itself to us, we must not reject it simply because it does not agree with the logical deductions of a reigning theory.

— Claude Bernard

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.

— Claude Bernard

From An Introduction to the Study of Experimental Medicine (1865), as translated by Henry Copley Greene (1957), 164.

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.

— Claude Bernard

From An Introduction to the Study of Experimental Medicine (1865), as translated by Henry Copley Greene (1957), 37.

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.

— Claude Bernard

From An Introduction to the Study of Experimental Medicine (1927, 1957), as translated by Henry Copley Greene (1957), 38. From the original French by Claude Bernard: “Ceux qui croient trop à leurs théories ne croient pas assez à celles des autres. Alors … ces contempteurs d'autrui … font des expériences que pour détruire une théorie, au lieu de les faire pour chercher la vérité.” (1865), 68. A Google translation gives: “Those who believe too much in their theories do not believe enough in those of others. So … these despisers of others … do experiments only to destroy a theory, instead of doing them to seek the truth.”

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.

— Claude Bernard

From An Introduction to the Study of Experimental Medicine (1927, 1957), as translated by Henry Copley Greene (1957), 38. Note: the ellipsis condenses the quote from two paragraphs, beginning with the same clause as another quote on this web page, beginning, “Men who have excessive faith….” From the original French by Claude Bernard: “Les hommes qui ont une foi excessive dans leurs théories … font de mauvaises observations parce qu'ils ne prennent dans les résultats de leurs expériences que ce qui convient à leur but en négligeant ce qui ne s'y rapporte pas, et en écartant bien soigneusement tout ce qui pourrait aller dans le sens de l'idée qu'ils veulent combattre.” (1865), 67-68. A Google translation gives: “Men who have excessive faith in their theories … make bad observations because they only take from the results of their experiments what suits their purpose, neglecting what does not relate to it, and carefully discarding everything that could go in the direction of the idea they want to fight.”

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.

— Claude Bernard

From An Introduction to the Study of Experimental Medicine (1927, 1957), as translated by Henry Copley Greene (1957), 38. From the original French by Claude Bernard: “Les hommes qui ont une foi excessive dans leurs théories ou dans leurs idées sont non-seulement mal disposés pour faire des découvertes, mais ils font aussi de très-mauvaises observations. Ils observent nécessairement avec une idée préconçue, et quand ils ont institué une expérience, ils ne veulent voir dans ses résultats qu'une confirmation de leur théorie. Ils défigurent ainsi l'observation et négligent souvent des faits très-importants, parce qu’ils ne concourent pas à leur but.” (1865), 68. A Google translation gives: “Men who have excessive faith in their theories or in their ideas are not only ill disposed to make discoveries, but they also make very bad observations. They necessarily observe with a preconceived idea, and when they have instituted an experiment, they only want to see in its results a confirmation of their theory. They thus disfigure observation and often neglect very important facts, because they do not contribute to their end.”

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.

— Claude Bernard

From An Introduction to the Study of Experimental Medicine (1865), as translated by Henry Copley Greene (1957), 165.

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.

— Claude Bernard

From An Introduction to the Study of Experimental Medicine (1865), as translated by Henry Copley Greene (1957), 165.

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

— Claude Bernard

An Introduction to the Study of Experimental Medicine (1865, translation 1927, 1957), 39.

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

— Claude Bernard

In An Introduction to the Study of Experimental Medicine (1927, 1957), 38, as translated by Henry Copley Greene. From the original French by Claude Bernard: “Il faut garder sa liberté d'esprit, et croire que dans la nature l'absurde suivant nos théories n'est pas toujours impossible.” (1865), 67. A Google translation gives: “You have to keep your freedom of mind, … and believe that in nature the absurd according to our theories is not always impossible.”

We must trust our observations or our theories only after experimental verification. If we trust too much, the mind becomes bound and cramped by the results of its own reasoning; it no longer has freedom of action, and so lacks the power to break away from that blind faith in theories which is only scientific superstition.

— Claude Bernard

From An Introduction to the Study of Experimental Medicine (1865), as translated by Henry Copley Greene (1957), 37.

We see, then, that the elements of the scientific method are interrelated. Facts are necessary materials; but their working up by experimental reasoning, i.e., by theory, is what establishes and really builds up science. Ideas, given form by facts, embody science. A scientific hypothesis is merely a scientific idea, preconceived or previsioned. A theory is merely a scientific idea controlled by experiment. Reasoning merely gives a form to our ideas, so that everything, first and last, leads back to an idea. The idea is what establishes, as we shall see, the starting point or the primum movens of all scientific reasoning, and it is also the goal in the mind's aspiration toward the unknown.

— Claude Bernard

From An Introduction to the Study of Experimental Medicine (1865), as translated by Henry Copley Greene (1957), 26.

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.

— Claude Bernard

From An Introduction to the Study of Experimental Medicine (1865), as translated by Henry Copley Greene (1957), 165.

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.

— Claude Bernard

From An Introduction to the Study of Experimental Medicine (1927, 1957), 164, as translated by Henry Copley Greene. From the original French by Claude Bernard: “Quand le fait qu’on rencontre est en opposition avec une théorie régnante, il faut accepter le fait et abandonner la théorie, lors même que celle-ci, soutenue par de grands noms, est généralement adoptée.” (1865), 287-288. A Google translation gives: “When the fact one encounters is in opposition to a reigning theory, one must accept the fact and abandon the theory, even when the latter, supported by great names, is generally adopted.”