"A physical theory is not an explanation. It is a system of mathematical propositions, deduced from a small number of principles, which aim to represent as simply, as completely, and as exactly as possible a set of experimental laws. […] Thus a true theory is not a theory which gives an explanation of physical appearances in conformity with reality; it is a theory which represents in a satisfactory manner a group of experimental laws. A false theory is not an attempt at an explanation based on assumptions contrary to reality; it is a ·group of propositions which do not agree with the experimental laws. Agreement with experiment is the sole criterion of truth for a physical theory." (Pierre-Maurice-Marie Duhem, "La théorie physique. Son objet, sa structure", 1906)
"Imagine the forehead of a bull, with the protuberances from
which the horns and ears start, and with the collars hollowed out between these
protuberances; but elongate these horns and ears without limit so that they
extend to infinity; then you will have one of the surfaces we wish to study. On
such a surface geodesics may show many different aspects. There are, first of
all, geodesics which close on themselves. There are some also which are never
infinitely distant from their starting point even though they never exactly
pass through it again; some turn continually around the right horn, others
around the left horn, or right ear, or left ear; others, more complicated,
alternate, in accordance with certain rules, the turns they describe around one
horn with the turns they describe around the other horn, or around one of the
ears. Finally, on the forehead of our bull with his unlimited horns and ears
there will be geodesics going to infinity, some mounting the right horn, others
mounting the left horn, and still others following the right or left ear. [...] If, therefore, a material point is thrown on the surface studied starting
from a geometrically given position with a geometrically given velocity,
mathematical deduction can determine the trajectory of this point and tell
whether this path goes to infinity or not. But, for the physicist, this
deduction is forever useless. When, indeed, the data are no longer known
geometrically, but are determined by physical procedures as precise as we may
suppose, the question put remains and will always remain unanswered."
"Indeed, a mathematical deduction is of no use to the physicist so long as it is limited to asserting that a given rigorously true proposition has for its consequence the rigorous accuracy of some such other proposition. To be useful to the physicist, it must still be proved that the second proposition remains approximately exact when the first is only approximately true. And even that does not suffice. The range of these two approximations must be delimited; it is necessary to fix the limits of error which can be made in the result when the degree of precision of the methods of measuring the data is known; it is necessary to define the probable error that can be granted the data when we wish to know the result within a definite degree of approximation." (Pierre-Maurice-Marie Duhem, "La théorie physique. Son objet, sa structure", 1906)
"Order, wherever it reigns, brings beauty with it. Theory not only renders the group of physical laws it represents easier to handle, more convenient, and more useful, but also more beautiful." (Pierre-Maurice-Marie Duhem, "La théorie physique. Son objet, sa structure", 1906)
"[...] the aim of physical theory is to become a natural classification, to establish among diverse experimental laws a logical coordination serving as a sort of image and reflection of the true order according to which the realities escaping us are organized." (Pierre-Maurice-Marie Duhem, "La théorie physique. Son objet, sa structure", 1906)
"The distinction between physics, which studies phenomena and their laws, and metaphysics, which seeks to know the essence of matter insofar as it is the cause of phenomena and the basis of laws, is deprived of any foundation. The mind does not start from the knowledge of phenomena to rise to the knowledge of matter; what it can know from the start is the very nature of matter, and thence the explanation of phenomena." (Pierre-Maurice-Marie Duhem, "La théorie physique. Son objet, sa structure", 1906)
"Theory is not solely an economical representation of experimental laws; it is also a classification of these laws. […] theory, by developing the numerous ramifications of the deductive reasoning which connects principles to experimental laws, establishes an order and a classification among these laws. It brings some laws together, closely arranged in the same group; it separates some of the others by placing them in two groups very far apart. Theory gives, so to speak, the table of contents and the chapter headings under which the science to be studied will be methodically divided, and it indicates the laws which are to be arranged under each of these chapters." (Pierre-Maurice-Marie Duhem, "La théorie physique. Son objet, sa structure", 1906)
"Thus, physical theory never gives us the explanation of experimental laws; it never reveals realities hiding under the sensible appearances; but the more complete it becomes, the more we apprehend that the logical order in which theory orders experimental laws is the reflection of an ontological order, the more we suspect that the relations it establishes among the data of observation correspond to real relations among things, and the more we feel that theory tends to be a natural classification." (Pierre-Maurice-Marie Duhem, "La théorie physique. Son objet, sa structure", 1906)
"But, once again, what the physical states as the result of an experiment is not the recital of observed facts, but the interpretation and the transposing of these facts into the ideal, abstract, symbolic world created by the theories he regards as established." (Pierre-Maurice-Marie Duhem, “The Aim and Structure of Physical Theory”, 1908)
"If the aim of physical theories is to explain experimental laws, theoretical physics is not an autonomous science; it is subordinate to metaphysics." (Pierre-Maurice-Marie DuhemDuhem, "The Aim and Structure of Physical Theory", 1908)
"It is impossible to follow the march of one of the greatest theories of physics, to see it unroll majestically its regular deductions starting from initial hypotheses, to see its consequences represent a multitude of experimental laws down to the smallest detail, without being charmed by the beauty of such a construction, without feeling keenly that such a creation of the human mind is truly a work of art." (Pierre-Maurice-Marie DuhemDuhem, "The Aim and Structure of Physical Theory", 1908)
"[...] physics makes progress because experiment constantly causes new disagreements to break out between laws and facts, and because physicists constantly touch up and modify laws in order that they may more faithfully represent the facts." (Pierre-Maurice-Marie Duhem, "The Aim and Structure of Physical Theory", 1908)
"The laws of physics are therefore provisional in that the symbols they relate too simple to represent reality completely." (Pierre-Maurice-Marie Duhem, "The Aim and Structure of Physical Theory", 1908)
“Order wherever it reigns, brings beauty with it. Theory not only renders the group of physical laws it represents easier to handle, more convenient, and more useful, but also more beautiful.” (Pierre-Maurice-Marie Duhem, “The Aim and Structure of Physical Theory”, 1908)"Physics makes progress because experiment constantly causes new disagreements to break out between laws and facts, and because physicists constantly touch up and modify laws in order that they may more faithfully represent the facts." (Pierre-Maurice-Marie Duhem, “The Aim and Structure of Physical Theory”, 1908)
"The laws of physics are therefore provisional in that the symbols they relate too simple to represent reality completely." (Pierre-Maurice-Marie Duhem, “The Aim and Structure of Physical Theory”, 1908)
"The sole purpose of physical theory is to provide a representation and classification of experimental laws; the only test permitting us to judge a physical theory and pronounce it good or bad is the comparison between the consequences of this theory and the experimental laws it has to represent and classify." (Pierre-Maurice-Marie Duhem, “The Aim and Structure of Physical Theory”, 1908)
"A theory of physics is not an explanation; it is a system of mathematical oppositions deduced from a small number of principles the aim of which is to represent as simply, as completely, and as exactly as possible, a group of experimental laws." (Pierre-Maurice-Marie Duhem)
"Physics is not a machine one can take apart; one cannot try each piece in isolation and wait, to adjust it, until its solidity has been minutely checked. Physical science is a system that must be taken as a whole. It is an organism no part of which can be made to function without the remotest parts coming into play, some more, some less, but all in some degree." (Pierre-Maurice-Marie Duhem)
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