Claude Bernard

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

"Science does not permit exceptions."

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

"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."

"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."

"Considered in itself, the experimental method is nothing but reasoning by whose help we methodically submit our ideas to experience,—the experience of facts."

"[T]he science of life […] is a superb and dazzlingly lighted hall which may be reached only by passing through a long and ghastly kitchen."

"In sciences of observation, man observes and reasons experimentally, but he does not experiment; and in this sense we might say that a science of observation is a passive science. In sciences of experimentation, man observes, but in addition he acts on matter, analyzes its properties and to his own advantage brings about the appearance of phenomena which doubtless always occur according to natural laws, but in conditions which nature often has not yet achieved. With the help 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 in the experimental sciences."

"Men who have excessive faith in their theories or ideas are not only ill prepared for making discoveries; they also make very poor observations."

"[T]hey 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."

"[T]he experimental method draws from within itself an impersonal authority which dominates science. It forces this authority even on great men.[…] Every period has its own sum total of errors and of truths. Certain mistakes are, in a sense, inherent in their period, so that only the subsequent progress of science can reveal them.… [T]he further science advances, the more it takes an impersonal form and detaches itself from the past."

"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.""

"[I]t is important to determine at what point to apply doubt, so as to distinguish it from scepticism, and to show how scientific doubt becomes an element of the greatest certainty. The sceptic disbelieves in science and believes in himself; he believes enough in himself to dare deny science and to assert that it is not subject to definite, fixed laws. The doubter is a true man of science; he doubts only himself and his interpretations, but he believes in science; in the experimental sciences, he even accepts a criterion of absolute scientific principle."

"Indeed, 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 phenomenon will no longer appear."

"[A] living organism is nothing but a wonderful machine."

"[S]cience, in humbling our pride, proportionately increases our power."

"[P]articular facts are never scientific; only generalization can establish science."

"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."

"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."

"[T]heories 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."

"Our language, in fact, is only approximate, and even in science it is so indefinite that if we lose sight of phenomena and cling to words, we are speedily outside of reality.… [W]e must always cling to phenomena and see in words only expressions empty of meaning, if the phenomena they represent are not definite, or if they are absent."

"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 sole happiness.… [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."

"True science teaches us to doubt and to abstain from ignorance."

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

"If I had to define life in a word, it would be: Life is creation."

"A modern poet has characterized the personality of art and the impersonality of science as follows: Art is I: Science is We."

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

"Schade, dass es vorbei ist."