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Mortimer Adler
Rogers Albritton
Alexander of Aphrodisias
Samuel Alexander
William Alston
Louise Antony
Thomas Aquinas
David Armstrong
Harald Atmanspacher
Robert Audi
Alexander Bain
Mark Balaguer
Jeffrey Barrett
William Belsham
Henri Bergson
George Berkeley
Isaiah Berlin
Richard J. Bernstein
Bernard Berofsky
Robert Bishop
Max Black
Susanne Bobzien
Emil du Bois-Reymond
Hilary Bok
Laurence BonJour
George Boole
Émile Boutroux
Michael Burke
Joseph Keim Campbell
Rudolf Carnap
Ernst Cassirer
David Chalmers
Roderick Chisholm
Randolph Clarke
Samuel Clarke
Anthony Collins
Antonella Corradini
Diodorus Cronus
Jonathan Dancy
Donald Davidson
Mario De Caro
Daniel Dennett
Jacques Derrida
René Descartes
Richard Double
Fred Dretske
John Dupré
John Earman
Laura Waddell Ekstrom
Herbert Feigl
John Martin Fischer
Owen Flanagan
Luciano Floridi
Philippa Foot
Alfred Fouilleé
Harry Frankfurt
Richard L. Franklin
Michael Frede
Gottlob Frege
Peter Geach
Edmund Gettier
Carl Ginet
Alvin Goldman
Nicholas St. John Green
H.Paul Grice
Ian Hacking
Ishtiyaque Haji
Stuart Hampshire
Sam Harris
William Hasker
Georg W.F. Hegel
Martin Heidegger
Thomas Hobbes
David Hodgson
Shadsworth Hodgson
Baron d'Holbach
Ted Honderich
Pamela Huby
David Hume
Ferenc Huoranszki
William James
Lord Kames
Robert Kane
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Tomis Kapitan
Jaegwon Kim
William King
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Christine Korsgaard
Saul Kripke
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Keith Lehrer
Gottfried Leibniz
Jules Lequyer
Michael Levin
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David Lewis
Peter Lipton
C. Lloyd Morgan
John Locke
Michael Lockwood
E. Jonathan Lowe
John R. Lucas
Alasdair MacIntyre
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James Martineau
Storrs McCall
Hugh McCann
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Michael McKenna
Brian McLaughlin
John McTaggart
Paul E. Meehl
Uwe Meixner
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Trenton Merricks
John Stuart Mill
Dickinson Miller
Thomas Nagel
Otto Neurath
Friedrich Nietzsche
John Norton
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Mark Twain
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G.H. von Wright
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R. Jay Wallace
Ted Warfield
Roy Weatherford
William Whewell
Alfred North Whitehead
David Widerker
David Wiggins
Bernard Williams
Timothy Williamson
Ludwig Wittgenstein
Susan Wolf


Michael Arbib
Walter Baade
Bernard Baars
Leslie Ballentine
Gregory Bateson
John S. Bell
Charles Bennett
Ludwig von Bertalanffy
Susan Blackmore
Margaret Boden
David Bohm
Niels Bohr
Ludwig Boltzmann
Emile Borel
Max Born
Satyendra Nath Bose
Walther Bothe
Hans Briegel
Leon Brillouin
Stephen Brush
Henry Thomas Buckle
S. H. Burbury
Donald Campbell
Anthony Cashmore
Eric Chaisson
Jean-Pierre Changeux
Arthur Holly Compton
John Conway
John Cramer
E. P. Culverwell
Charles Darwin
Richard Dawkins
Terrence Deacon
Lüder Deecke
Richard Dedekind
Louis de Broglie
Max Delbrück
Abraham de Moivre
Paul Dirac
Hans Driesch
John Eccles
Arthur Stanley Eddington
Gerald Edelman
Paul Ehrenfest
Albert Einstein
Hugh Everett, III
Franz Exner
Richard Feynman
R. A. Fisher
Joseph Fourier
Philipp Frank
Lila Gatlin
Michael Gazzaniga
GianCarlo Ghirardi
J. Willard Gibbs
Nicolas Gisin
Paul Glimcher
Thomas Gold
Brian Goodwin
Joshua Greene
Jacques Hadamard
Patrick Haggard
Stuart Hameroff
Augustin Hamon
Sam Harris
Hyman Hartman
John-Dylan Haynes
Donald Hebb
Martin Heisenberg
Werner Heisenberg
John Herschel
Art Hobson
Jesper Hoffmeyer
E. T. Jaynes
William Stanley Jevons
Roman Jakobson
Pascual Jordan
Ruth E. Kastner
Stuart Kauffman
Martin J. Klein
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Rolf Landauer
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Pierre-Simon Laplace
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Benjamin Libet
Seth Lloyd
Hendrik Lorentz
Josef Loschmidt
Ernst Mach
Donald MacKay
Henry Margenau
James Clerk Maxwell
Ernst Mayr
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Ulrich Mohrhoff
Jacques Monod
Emmy Noether
Abraham Pais
Howard Pattee
Wolfgang Pauli
Massimo Pauri
Roger Penrose
Steven Pinker
Colin Pittendrigh
Max Planck
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Henri Poincaré
Daniel Pollen
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Hans Primas
Adolphe Quételet
Juan Roederer
Jerome Rothstein
David Ruelle
Erwin Schrödinger
Aaron Schurger
Claude Shannon
David Shiang
Herbert Simon
Dean Keith Simonton
B. F. Skinner
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John Stachel
Henry Stapp
Tom Stonier
Antoine Suarez
Leo Szilard
Max Tegmark
William Thomson (Kelvin)
Giulio Tononi
Peter Tse
Vlatko Vedral
Heinz von Foerster
John von Neumann
John B. Watson
Daniel Wegner
Steven Weinberg
Paul A. Weiss
John Wheeler
Wilhelm Wien
Norbert Wiener
Eugene Wigner
E. O. Wilson
H. Dieter Zeh
Ernst Zermelo
Wojciech Zurek
Konrad Zuse
Fritz Zwicky


Free Will
Mental Causation
James Symposium
Mechanism and Experience
("Le mécanisme et l'expérience", Revue de Metaphysique et de Morale 1, pp. 534-7 (1893); English translation, Stephen Brush, Kinetic Theory, vol.2, p.203)

SUMMARY The advocates of the mechanistic conception of the universe have met with several obstacles in their attempts to reconcile mechanism with the facts of experience. In the mechanistic hypothesis, all phenomena must be reversible, while experience shows that many phenomena are irreversible. It has been suggested that the apparent irreversibility of natural phenomena is due merely to the fact that molecules are too small and too numerous for our gross senses to deal with them, although a "Maxwell demon" could do so and would thereby be able to prevent irreversibility.

The kinetic theory of gases is up to now the most serious attempt to reconcile mechanism and experience, but it is still faced with the difficulty that a mechanical system cannot tend toward a permanent final state but must always return eventually to a state very close to its initial state. This difficulty can be overcome only if one is willing to assume that the universe does not tend irreversibly to a final state, as seems to be indicated by experience, but will eventually regenerate itself and reverse the second law of thermodynamics.

Everyone knows the mechanistic conception of the universe which has seduced so many good men, and the different forms in which it has been dressed. Some represent the material world as being composed of atoms which move in straight lines because of their inertia; the velocity and direction of this motion cannot change except when two atoms collide.

Others allow action at a distance, and suppose that the atoms exert on each other an attraction (or a repulsion) which depends on their distance according to some law. The first viewpoint is clearly only a particular case of the second; what I am going to say will be as true of one as of the other. The most important conclusions apply also to Cartesian mechanism, in which one assumes a continuous matter.

It would perhaps be appropriate to discuss here the metaphysical difficulties that underlie these conceptions; but I do not have the necessary authority for that. Rather than discussing with the readers of this review that which they know better than I do, I prefer to speak of subjects with which they are less familiar, but which may interest them indirectly.

I am going to concern myself with the obstacles which the mechanists have encountered when they wished to reconcile their system with experimental facts, and the efforts which they have made to overcome or circumvent them.

In the mechanistic hypothesis, all phenomena must be reversible; for example, the stars might traverse their orbits in the retrograde sense without violating Newton's law; this would be true for any law of attraction whatever. This is therefore not a fact peculiar to astronomy; reversibility is a necessary consequence of all mechanistic hypotheses.

Experience provides on the contrary a number of irreversible phenomena. For example, if one puts together a warm and a cold body, the former will give up its heat to the latter; the opposite phenomenon never occurs. Not only will the cold body not return to the warm one the heat which it has taken away when it is in direct contact with it; no matter what artifice one may employ, using other intervening bodies, this restitution will be impossible, at least unless the gain thereby realized is compensated by an equivalent or large loss. In other words, if a system of bodies can pass from state A to state B by a certain path, it cannot return from B to A, either by the same path or by a different one. It is this circumstance that one describes by saying that not only is there not direct reversibility, but also there is not even indirect reversibility.

There have been many attempts to escape this contradiction; first there was Helmholtz's hypothesis of "hidden movements". Recall the experiment made by Foucault and Pantheon with a very long pendulum. This apparatus seems to turn slowly, indicating the rotation of the earth. An observer who does not know about the movement of the earth would certainly conclude that mechanical phenomena are irreversible. The pendulum always turns in the same sense, and there is no way to make it turn in the opposite sense; to do that it would be necessary to change the sense of rotation of the earth. Such a change is of course impractical, but for us it is conceivable; it would not be so for a man who believed our planet to be immobile.

Can one not imagine that there exist similar motions in the molecular world, which are hidden from us, which we have not taken account of, and of which we cannot change the sense? This explanation is seductive, but it is insufficient; it shows why there is not direct reversibility; but one can show that it still requires indirect reversibility.

The English have proposed a completely different hypothesis. To explain it, I will make use of a comparison: if one had a hectolitre of wheat and a grain of barley, it would be easy to hide this grain in the middle of the wheat; but it would be almost impossible to find it again, so that the phenomenon appears to be in a sense irreversible. This is because the grains are small and numerous; the apparent irreversibility of natural phenomena is likewise due to the fact that the molecules are too small and too numerous for our gross senses to deal with them.

To clarify this explanation, Maxwell introduced the fiction of a "demon" whose eyes are sharp enough to distinguish the molecules, and whose hands are small and fast enough to grab them. For such a demon, if one believes the mechanists, there would be no difficulty in making heat pass from a cold to a warm body.

The development of this idea has given rise to the kinetic theory of gases, which is up to now the most serious attempt to reconcile mechanism and experience, But all the difficulties have not been overcome.

this is Poincaré's theorem from his study of the three-body problem
A theorem, easy to prove, tells us that a bounded world, governed only by the laws of mechanics, will always pass through a state very close to its initial state. On the other hand, according to accepted experimental laws (if one attributes absolute validity to them, and if one is willing to press their consequences to the extreme), the universe tends toward a certain final state, from which it will never depart. In this final state, which will be a kind of death, all bodies will be at rest at the same temperature.

I do not know if it has been remarked that the English kinetic theories can extricate themselves from this contradiction. The world, according to them, tends at first toward a state where it remains for a long time without apparent change; and this is consistent with experience; but it does not remain that way forever, if the theorem cited above is not violated; it merely stays there for an enormously long time, a time which is longer the more numerous are the molecules. This state will not be the final death of the universe, but a sort of slumber, from which it will awake after millions of millions of centuries. According to this theory, to see heat pass from a cold body to a warm one, it will not be necessary to have the acute vision, the intelligence, and the dexterity of Maxwell's demon; it will suffice to have a little patience.

One would like to be able to stop at this point and hope that some day the telescope will show us a world in the process of waking up, where the laws of thermodynamics are reversed.

Unfortunately, other contradictions arise; Maxwell made ingenious efforts to conquer them. But I am not sure that he succeeded. The problem is so complicated that it is impossible to treat it with complete rigour. One is then forced to make certain simplifying hypotheses; are they legitimate, are they self-consistent? I do not believe they are. I do not wish to discuss them here; but there is no need for a long discussion in order to challenge an argument of which the premises are apparently in contradiction with the conclusion, where one finds in effect reversibility in the premises and irreversibility in the conclusion.

Thus the difficulties that concern us have not been overcome, and it is possible that they never will be. This would amount to a definite condemnation of mechanism, if the experimental laws should prove to be distinctly different from the theoretical ones.

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