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Home > Dictionary of Science Quotations > Scientist Names Index B > Claude Bernard Quotes > Cause

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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.



A great surgeon performs operations for stone by a single method; later he makes a statistical summary of deaths and recoveries, and he concludes from these statistics that the mortality law for this operation is two out of five. Well, I say that this ratio means literally nothing scientifically and gives us no certainty in performing the next operation; for we do not know whether the next case will be among the recoveries or the deaths. What really should be done, instead of gathering facts empirically, is to study them more accurately, each in its special determinism. We must study cases of death with great care and try to discover in them the cause of mortal accidents so as to master the cause and avoid the accidents.
— Claude Bernard
From An Introduction to the Study of Experimental Medicine (1865), as translated by Henry Copley Greene (1957), 137-138. (Note that Bernard overlooks how the statistical method can be useful: a surgeon announcing a mortality rate of 40% invites comparison. A surgeon with worse outcomes should adopt this method. If a surgeon has a better results, that method should be adopted.)
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A physician’s subject of study is necessarily the patient, and his first field for observation is the hospital. But if clinical observation teaches him to know the form and course of diseases, it cannot suffice to make him understand their nature; to this end he must penetrate into the body to find which of the internal parts are injured in their functions. That is why dissection of cadavers and microscopic study of diseases were soon added to clinical observation. But to-day these various methods no longer suffice; we must push investigation further and, in analyzing the elementary phenomena of organic bodies, must compare normal with abnormal states. We showed elsewhere how incapable is anatomy alone to take account of vital phenenoma, and we saw that we must add study of all physico-chemical conditions which contribute necessary elements to normal or pathological manifestations of life. This simple suggestion already makes us feel that the laboratory of a physiologist-physician must be the most complicated of all laboratories, because he has to experiment with phenomena of life which are the most complex of all natural phenomena.
— Claude Bernard
From An Introduction to the Study of Experimental Medicine (1865), as translated by Henry Copley Greene (1957), 140-141.
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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.
— Claude Bernard
From An Introduction to the Study of Experimental Medicine (1865), as translated by Henry Copley Greene (1957), 134-137.
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By destroying the biological character of phenomena, the use of averages in physiology and medicine usually gives only apparent accuracy to the results. From our point of view, we may distinguish between several kinds of averages: physical averages, chemical averages and physiological and pathological averages. If, for instance, we observe the number of pulsations and the degree of blood pressure by means of the oscillations of a manometer throughout one day, and if we take the average of all our figures to get the true or average blood pressure and to learn the true or average number of pulsations, we shall simply have wrong numbers. In fact, the pulse decreases in number and intensity when we are fasting and increases during digestion or under different influences of movement and rest; all the biological characteristics of the phenomenon disappear in the average. Chemical averages are also often used. If we collect a man's urine during twenty-four hours and mix all this urine to analyze the average, we get an analysis of a urine which simply does not exist; for urine, when fasting, is different from urine during digestion. A startling instance of this kind was invented by a physiologist who took urine from a railroad station urinal where people of all nations passed, and who believed he could thus present an analysis of average European urine! Aside from physical and chemical, there are physiological averages, or what we might call average descriptions of phenomena, which are even more false. Let me assume that a physician collects a great many individual observations of a disease and that he makes an average description of symptoms observed in the individual cases; he will thus have a description that will never be matched in nature. So in physiology, we must never make average descriptions of experiments, because the true relations of phenomena disappear in the average; when dealing with complex and variable experiments, we must study their various circumstances, and then present our most perfect experiment as a type, which, however, still stands for true facts. In the cases just considered, averages must therefore be rejected, because they confuse, while aiming to unify, and distort while aiming to simplify. Averages are applicable only to reducing very slightly varying numerical data about clearly defined and absolutely simple cases.
— Claude Bernard
From An Introduction to the Study of Experimental Medicine (1865), as translated by Henry Copley Greene (1957), 134-135.
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Constant, or free, life is the third form of life; it belongs to the most highly organized animals. In it, life is not suspended in any circumstance, it unrolls along a constant course, apparently indifferent to the variations in the cosmic environment, or to the changes in the material conditions that surround the animal. Organs, apparatus, and tissues function in an apparently uniform manner, without their activity undergoing those considerable variations exhibited by animals with an oscillating life. This because in reality the internal environment that envelops the organs, the tissues, and the elements of the tissues does not change; the variations in the atmosphere stop there, so that it is true to say that physical conditions of the environment are constant in the higher animals; it is enveloped in an invariable medium, which acts as an atmosphere of its own in the constantly changing cosmic environment. It is an organism that has placed itself in a hot-house. Thus the perpetual changes in the cosmic environment do not touch it; it is not chained to them, it is free and independent.
— Claude Bernard
Lectures on the Phenomena of Life Common to Animals and Plants (1878), trans. Hebbel E. Hoff, Roger Guillemin and Lucienne Guillemin (1974), 83.
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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.
— Claude Bernard
From An Introduction to the Study of Experimental Medicine (1865), as translated by Henry Copley Greene (1957),10.
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First causes are outside the realm of science.
— Claude Bernard
From An Introduction to the Study of Experimental Medicine (1865), as translated by Henry Copley Greene (1957), 66.
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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..
— Claude Bernard
From An Introduction to the Study of Experimental Medicine (1865), as translated by Henry Copley Greene (1957), 138-140.
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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
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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.
— Claude Bernard
From An Introduction to the Study of Experimental Medicine (1865), as translated by Henry Copley Greene (1957), 146.
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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.
— Claude Bernard
…...
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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.
— Claude Bernard
From An Introduction to the Study of Experimental Medicine (1865), as translated by Henry Copley Greene (1957), 138.
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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.
— Claude Bernard
From An Introduction to the Study of Experimental Medicine (1865), as translated by Henry Copley Greene (1957), 18. A footnote cites Laplace, Système du monde, Chap. 2.
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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.”
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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.”
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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.
— Claude Bernard
From An Introduction to the Study of Experimental Medicine (1865), as translated by Henry Copley Greene (1957), 55.
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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.
— Claude Bernard
Sur le Méchanisme de la Fonction du Sucre dans Ie Foie (1857), 583. Translated in Joseph S. Fruton, Proteins, Enzymes, Genes: The Interplay of Chemistry and Biology (1999), 340.
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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.
— Claude Bernard
From An Introduction to the Study of Experimental Medicine (1865), as translated by Henry Copley Greene (1957), 139.
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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.
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See also:
  • 12 Jul - short biography, births, deaths and events on date of Bernard's birth.
  • Claude Bernard - context of quote The alchemists founded chemistry - Medium image (500 x 350 px)
  • Claude Bernard - context of quote “The alchemists founded chemistry” - Large image (800 x 600 px)
  • Claude Bernard - context of quote The experimenter - Medium image (500 x 350 px)
  • Claude Bernard - context of quote The experimenter - Large image (800 x 600 px)
  • Claude Bernard - context of quote Make experiments to … control our ideas - Medium image (500 x 350 px)
  • Claude Bernard - context of quote Make experiments to … control our ideas - Large image (800 x 600 px)

Carl Sagan Thumbnail In science it often happens that scientists say, 'You know that's a really good argument; my position is mistaken,' and then they would actually change their minds and you never hear that old view from them again. They really do it. It doesn't happen as often as it should, because scientists are human and change is sometimes painful. But it happens every day. I cannot recall the last time something like that happened in politics or religion. (1987) -- Carl Sagan
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