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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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Claude Bernard quote Make experiments to … control our ideas

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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.

— Claude Bernard

From Introduction à l'étude de la médecine expérimentale (1865), 67-68. Translation from Henry Copley Green, An Introduction to the Study of Experimental Medicine (1957), 38. Bernard footnoted that he had expressed this idea earlier in Leçons sur les propriétés et les altérations des liquides de l’organisme (1859), Première leçon.

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.

Une idée anticipée ou une hypothèse est donc le point de départ nécessaire de tout raisonnement expérimental. Sans cela on ne saurait faire aucune investigation ni s’instruire ; on ne pourrait qu’entasser des observations stériles. Si l’on expérimentait sans idée préconçue, on irait à l’aventure; mais d’un autre côté, ainsi que nous l’avons dit ailleurs, si l’on observait avec des idées préconçues, on ferait de mauvaises observations.
An anticipative idea or an hypothesis is, then, the necessary starting point for all experimental reasoning. Without it, we could not make any investigation at all nor learn anything; we could only pile up sterile observations. If we experimented without a preconceived idea, we should move at random.
[Also seen translated as:] A hypothesis is … the obligatory starting point of all experimental reasoning. Without it no investigation would be possible, and one would learn nothing: one could only pile up barren observations. To experiment without a preconceived idea is to wander aimlessly.

— Claude Bernard

Original work in French, Introduction à l'Étude de la Médecine Expérimentale (1865). English translation by Henry Copley Green in An Introduction to the Study of Experimental Medicine (1927, 1957), 32. Alternate translation in Peter Medawar, 'Hypothesis and Imagination', collected in The Strange Case of the Spotted Mice and Other Classic Essays on Science (1974), 30.

A fact is nothing in itself. It has value only for the idea connected with it or through the proof that it furnishes.

— Claude Bernard

In An Introduction to the Study of Experimental Medicine (1927, 1957), 53, as translated by Henry Copley Greene. From the original French by Claude Bernard: “Un fait n’est rien par lui-même, il ne vaut que par l’idée qui s’y rattache ou par la preuve qu’il fournit.” (1865), 93.

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 science the important thing is to modify and change one's ideas as science advances.

— Claude Bernard

As given by in Bertha McCool, 'The Development of Embryology', Bios (Oct 1935), 6, No. 3, 303. Also in Rudolf Franz Flesch, The Art of Clear Thinking (1951), 122. Webmaster has also seen this attributed to Herbert Spencer, but has yet found such examples date only after 1997. If you know the primary source from Bernard, please contact Webmaster.

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.

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.

— Claude Bernard

An Introduction to the Study of Experimental Medicine (1865, translation 1927, 1957), 23.

Man is naturally metaphysical and arrogant, and is thus capable of believing that the ideal creations of his mind, which express his feelings, are identical with reality. From this it follows that the experimental method is not really natural to him.

— Claude Bernard

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.

— Claude Bernard

From An Introduction to the Study of Experimental Medicine (1865), as translated by Henry Copley Greene (reprint 1999), 42.

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.”

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.

— Claude Bernard

In An Introduction to the Study of Experimental Medicine (1865).

We must…never be too much absorbed by the thought we are pursuing, nor deceive ourselves about the value of our ideas or scientific theories.

— Claude Bernard

In An Introduction to the Study of Experimental Medicine (1927, 1957), 167, as translated by Henry Copley Greene. From the original French by Claude Bernard: “On ne doit donc jamais être trop absorbé par la pensée qu’on poursuit, ni s’illusionner sur la valeur de ses idées ou de ses théories scientifiques.” (1865), 294.

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.

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.

— Claude Bernard

From An Introduction to the Study of Experimental Medicine (1865), as translated by Henry Copley Greene (1957), 164-165.