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Philosophers

Mortimer Adler
Rogers Albritton
Alexander of Aphrodisias
G.E.M.Anscombe
Anselm
Thomas Aquinas
Aristotle
David Armstrong
Augustine
J.L.Austin
A.J.Ayer
Alexander Bain
Mark Balaguer
William Belsham
Henri Bergson
Isaiah Berlin
Bernard Berofsky
Susanne Bobzien
Emil du Bois-Reymond
George Boole
Émile Boutroux
F.H.Bradley
C.D.Broad
C.A.Campbell
Joseph Keim Campbell
Carneades
Ernst Cassirer
Roderick Chisholm
Chrysippus
Cicero
Randolph Clarke
Samuel Clarke
Anthony Collins
Diodorus Cronus
Donald Davidson
Democritus
Daniel Dennett
René Descartes
Richard Double
Fred Dretske
John Earman
Laura Waddell Ekstrom
Epictetus
Epicurus
Herbert Feigl
John Martin Fischer
Owen Flanagan
Luciano Floridi
Philippa Foot
Alfred Fouilleé
Harry Frankfurt
Richard L. Franklin
Michael Frede
Carl Ginet
Nicholas St. John Green
H.Paul Grice
Ian Hacking
Ishtiyaque Haji
Stuart Hampshire
W.F.R.Hardie
R.M.Hare
Georg W.F. Hegel
Martin Heidegger
R.E.Hobart
Thomas Hobbes
David Hodgson
Shadsworth Hodgson
Ted Honderich
Pamela Huby
David Hume
Ferenc Huoranszki
William James
Lord Kames
Robert Kane
Immanuel Kant
Tomis Kapitan
William King
Christine Korsgaard
Keith Lehrer
Gottfried Leibniz
Leucippus
Michael Levin
C.I.Lewis
David Lewis
Peter Lipton
John Locke
Michael Lockwood
John R. Lucas
Lucretius
James Martineau
Hugh McCann
Colin McGinn
Michael McKenna
Paul E. Meehl
Alfred Mele
John Stuart Mill
Dickinson Miller
G.E.Moore
Thomas Nagel
Friedrich Nietzsche
P.H.Nowell-Smith
Robert Nozick
William of Ockham
Timothy O'Connor
David F. Pears
Charles Sanders Peirce
Derk Pereboom
Steven Pinker
Plato
Karl Popper
H.A.Prichard
Hilary Putnam
Willard van Orman Quine
Frank Ramsey
Ayn Rand
Thomas Reid
Charles Renouvier
Nicholas Rescher
C.W.Rietdijk
Josiah Royce
Bertrand Russell
Paul Russell
Gilbert Ryle
T.M.Scanlon
Moritz Schlick
Arthur Schopenhauer
John Searle
Wilfrid Sellars
Henry Sidgwick
Walter Sinnott-Armstrong
J.J.C.Smart
Saul Smilansky
Michael Smith
L. Susan Stebbing
George F. Stout
Galen Strawson
Peter Strawson
Eleonore Stump
Richard Taylor
Kevin Timpe
Peter van Inwagen
Manuel Vargas
John Venn
Kadri Vihvelin
Voltaire
G.H. von Wright
David Foster Wallace
R. Jay Wallace
W.G.Ward
Ted Warfield
Roy Weatherford
Alfred North Whitehead
David Widerker
David Wiggins
Bernard Williams
Ludwig Wittgenstein
Susan Wolf

Scientists

Michael Arbib
Bernard Baars
John S. Bell
Charles Bennett
Margaret Boden
David Bohm
Neils Bohr
Ludwig Boltzmann
Emile Borel
Max Born
Leon Brillouin
Stephen Brush
Henry Thomas Buckle
Donald Campbell
Anthony Cashmore
Eric Chaisson
Jean-Pierre Changeux
Arthur Holly Compton
John Conway
E. H. Culverwell
Charles Darwin
Abraham de Moivre
Paul Dirac
John Eccles
Arthur Stanley Eddington
Paul Ehrenfest
Albert Einstein
Richard Feynman
Joseph Fourier
Michael Gazzaniga
GianCarlo Ghirardi
Nicolas Gisin
Thomas Gold
A.O.Gomes
Joshua Greene
Jacques Hadamard
Patrick Haggard
Augustin Hamon
Sam Harris
Martin Heisenberg
Werner Heisenberg
William Stanley Jevons
Pascual Jordan
Simon Kochen
Stephen Kosslyn
Rolf Landauer
Alfred Landé
Pierre-Simon Laplace
David Layzer
Benjamin Libet
Josef Loschmidt
Ernst Mach
Henry Margenau
James Clerk Maxwell
Ernst Mayr
Jacques Monod
Roger Penrose
Steven Pinker
Max Planck
Henri Poincaré
Adolphe Quételet
Jerome Rothstein
Erwin Schrödinger
Claude Shannon
Herbert Simon
Dean Keith Simonton
B. F. Skinner
Henry Stapp
Antoine Suarez
Leo Szilard
William Thomson (Kelvin)
John von Neumann
Daniel Wegner
Steven Weinberg
Norbert Wiener
Eugene Wigner
E. O. Wilson
Ernst Zermelo
 
Karl Popper
Popper wrote extensively on the problem of determinism and free will, researched many earlier thinkers on the subject, and formulated his own "evolutionary" model of free will. In his Arthur Holly Compton lecture, Of Clouds and Clocks, delivered at Washington University in St. Louis in April 1965, he noted that earlier thinkers had seen the only alternative to determinism as chance.

This is the classic argument against free will, that it comes to a stark choice between determinism or indeterminism.

Hume found nothing between chance and necessity, and Eddington had said, there is "no halfway house" between randomness and determinism.

But note that Popper may have been inspired by Arthur Holly Compton himself, who said an "act of choice [adds] a factor not supplied by the physical conditions...determining what will occur." See Compton's Atlantic Monthly article.

In his dialogues with John Eccles, (The Self and Its Brain, 1977), at first Popper dismissed quantum mechanics as being no help with free will, but later describes a two-stage model that parallels Darwinian evolution, with genetic mutations being probabilistic and involving quantum uncertainty.

"People who do not agree with determinism are usually viewed with suspicion by rationalists who are afraid that if we accept indeterminism, we may be committed to accepting the doctrine of Free Will, and may thus become involved in theological arguments about the Soul and Divine Grace. I usually avoid talking about free will, because I am not clear enough about what it means, and I even suspect that our intuition of a free will may mislead us. Nevertheless, I think that determinism is a theory which is untenable on many grounds, and that we have no reason whatever to accept it. Indeed, I think that it is important for us to get rid of the determinist element in the rationalist tradition. It is not only untenable, but it creates endless trouble for us. It is, for this reason, important to realize that indeterminism - that is, the denial of determinism - does not necessarily involve us in any doctrine about our 'will' or about 'responsibility'. (Popper, Conjectures and Refutations, 1962, Harper, 1968, p.123)

"The idea that the only alternative to determinism is just sheer chance was taken over by Schlick, together with many of his views on the subject, from Hume, who asserted that 'the removal' of what he called 'physical necessity' must always result in
'the same thing with chance. As objects must either be conjoin'd or not, . . . 'tis impossible to admit of any medium betwixt chance and an absolute necessity'.
"I shall later argue against this important doctrine according to which the alternative to determinism is sheer chance. Yet I must admit that the doctrine seems to hold good for the quantum-theoretical models which have been designed to explain, or at least to illustrate, the possibility of human freedom. This seems to be the reason why these models are so very unsatisfactory.

"Compton himself designed such a model, though he did not particularly like it. It uses quantum indeterminacy, and the unpredictability of a quantum jump, as a model of a human decision of great moment. It consists of an amplifier which amplifies the effect of a single quantum jump in such a way that it may either cause an explosion or destroy the relay necessary for bringing the explosion about. In this way one single quantum jump may be equivalent to a major decision. But in my opinion the model has no similarity to any rational decision. It is, rather, a model of a kind of decision-making where people who cannot make up their minds say: 'Let us toss a penny.' In fact, the whole apparatus for amplifying a quantum jump seems rather unnecessary: tossing a penny, and deciding on the result of the toss whether or not to pull a trigger, would do just as well. And there are of course computers,with built-in penny-tossing devices for producing random results, where such are needed.

"It may perhaps be said that some of our decisions are like penny-tosses: they are snap-decisions, taken without deliberation, since we often do not have enough time to deliberate. A driver or a pilot has sometimes to take a snap-decision like this; and if he is well trained, or jug-lucky, the result may be satisfactory; otherwise not.

"I admit that the quantum-jump model may be a model for such snap decisions; and I even admit that it is conceivable that something like the amplification of a quantum jump may actually happen in our brains if we make a snap-decision. But are snap-decisions really so very interesting? Are they characteristic of human behaviour - of rational human behaviour?

"I do not think so; and I do not think that we shall get much further with quantum jumps. They are just the kind of examples which seem to lend support to the thesis of Hume and Schlick that perfect chance is the only altenative to perfect determinism. What we need for understanding rational human behaviour and indeed, animal behaviour is something intermediate in character between perfect chance and perfect determinism - something intermediate between perfect clouds and perfect clocks.

"Hume's and Schlick's ontological thesis that there cannot exist anything intermediate between chance and determinism seems to me not only highly dogmatic (not to say doctrinaire) but clearly absurd; and it is understandable only on the assumption that they believed in a complete determinism in which chance has no status except as a symptom of our ignorance. (But even then it seems to me absurd, for there is, clearly, something like partial knowledge, or partial ignorance.)" (Objective Knowledge, Of Clouds and Clocks, 1972, p. 227ff)

Popper replying to John Eccles:
"First of all, I do of course agree that quantum theoretical indeterminacy in a sense cannot help, because this leads merely to probabilistic laws, and we do not wish to say that such things as free decisions are just probabilistic affairs.

"The trouble with quantum mechanical indeterminacy is twofold. First, it is probabilistic, and this doesn't help us much with the free-will problem, which is not just a chance affair. Second, it only gives us indeterminism, not openness to World 2 [Popper's Mind World]. However, in a roundabout way I do think that one may make use of quantum theoretical indeterminacy without committing oneself to the thesis that free-will decisions are probabilistic affairs.

Here Popper compares new ideas to variation in the gene pool due to random mutations followed by natural selection, as William James had done in 1880.
"New ideas have a striking similarity to genetic mutations. Now, let us look for a moment at genetic mutations. Mutations are, it seems, brought about by quantum theoretical indeterminacy (including radiation effects). Accordingly, they are also probabilistic and not in themselves originally selected or adequate, but on them there subsequently operates natural selection which eliminates inappropriate mutations. Now we could conceive of a similar process with respect to new ideas and to free-will decisions, and similar things.
Here Popper clearly conceptualizes the two-stage Cogito model already seen by James and Poincaré over fifty years earlier
That is to say, a range of possibilities is brought about by a probabilistic and quantum mechanically characterized set of proposals, as it were - of possibilities brought forward by the brain. On these there then operates a kind of selective procedure which eliminates those proposals and those possibilities which are not acceptable to the mind, anchored in World 3 [the world of human knowledge and artifacts, our Sum], which tries them out in World 3 and checks them by World 3 standards. This may perhaps be the way in which these things take place, and it was for this reason that I so much liked the suggestion about the inhibitory neurones working like a sculptor who cuts away and discards part of the stone in order to form his statue.
A few years earlier, Popper had called for a combination of randomness and control to explain freedom, though not yet explicitly, as is needed, in two stages with random chance before a controlled decision.
"freedom is not just chance but, rather, the result of a subtle interplay between something almost random or haphazard, and something like a restrictive or selective control"

(Objective Knowledge, Of Clouds and Clocks, 1972, p. 232)

For those extreme libertarians who prefer a traditional definition of freedom as pure chance (liberum arbitrium indifferentiae), we can offer free will as Popper's interplay between chance and control.

In 1977 Popper gave the first Darwin Lecture, at Darwin College, Cambridge. He called it Natural Selection and the Emergence of Mind. In it he said he had changed his mind (a rare admission by a philosopher) about two things. First he now thought that natural selection was not a "tautology" that made it an unfalsifiable theory. Second, he had come to accept the random variation and selection of ideas as a model of free will.

The selection of a kind of behavior out of a randomly offered repertoire may be an act of choice, even an act of free will. I am an indeterminist; and in discussing indeterminism I have often regretfully pointed out that quantum indeterminacy does not seem to help us;1 for the amplification of something like, say, radioactive disintegration processes would not lead to human action or even animal action, but only to random movements.

This is now the leading two-stage model of free will.
I have changed my mind on this issue.2 A choice process may be a selection process, and the selection may be from some repertoire of random events, without being random in its turn. This seems to me to offer a promising solution to one of our most vexing problems, and one by downward causation.

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