Hilary Putnam

Hilary Whitehall Putnam (born July 31, 1926) is a key figure in the philosophy of mind and many other areas of philosophy during the 20th century. After receiving his AB (undergraduate degree) from the University of Pennsylvania and PhD from UCLA (under Hans Reichenbach), he taught at Northwestern, Princeton, MIT, and Harvard, where he is now Cogan University Professor emeritus. While an undergraduate at the University of Pennsylvania, Putnam was a member of the Philomathean Society, the oldest US literary society.

Putnam has earned a reputation for changing his mind frequently during the course of his career, and he has written on so many diverse topics that it is often difficult to sort out his views. Some regard this as cause for ridicule; others admire his courage in admitting his mistakes and submitting his own views to intense criticism.

Philosophy of mind

Multiple Realizability

Putnam is probably most famous for his extraordinary, original contributions to the philosophy of mind. In particular, one of Putnam's most important and enduring contributions to this field is his formulation of the hypothesis of multiple realizability. The locus classicus of the thesis of multiple realizability is to be found in several papers published by Putnam in the late 1960's. In these papers, he argued that, contrary to the famous claim of the type-identity theory, it is not necessarily true that "pain is identical to C-fibre firing." It is quite possible, and indeed probable, that pain corresponds to, or is at least correlated with, completely different physical states of the nervous system in different organisms and yet they all experience the same mental state of "being in pain." Putnam cited numerous examples from all over the animal kingdom to illustrate his thesis. Is it likely, he asked, that the brain structures of all mammals, reptiles, birds, amphibians and molluscs realize pain, or other mental states, in exactly the same way? Do they even have the same brain structures? Clearly not, if we are to believe the evidence furnished by comparative neuroanatomy and neurophysiology. How is it possible then that they can share the same mental states and properties? The answer had to be that these mental kinds were realized by different physical states in different species. Putnam then took his argument a step further, asking about such things as the nervous systems of alien beings, artificially-intelligent robots and silicon-based life forms. Should such hypothetical entities be considered a priori incapable of experiencing pain just because they did not possess the same neurochemistry as humans? Putnam concluded that type-identity and other reductive theorists had been making an extremely "ambitious" and "highly implausible" conjecture which could be disproven with just one example of multiple realizability. This is sometimes referred to as the likelihood argument.

Putnam also formulated a complementary argument based on what he called functional isomorphism. He defined the concept in these terms: "Two systems are functionally isomorphic if there is a correspondence between the states of one and the states of the other that preserves functional relations." So, in the case of computers, two machines are functionally isomorphic if and only if the sequential relations among states in the first are exactly mirrored by the sequential relations among states in the other. Therefore, a computer made out of silicon chips and a computer made out of cogs and wheels can be functionally isomorphic but constitutionally diverse. Functional isomorphism implies multiple realizability. This is sometimes referred to as an "a priori argument".

Jerry Fodor, Putnam, and others immediately noted that, along with being a very effective argument against type-identity theories, multiple realizability implied that any low-level explanation of higher-level mental phenomena would be insufficiently abstract and general. Functionalism, which attempts to identify mental kinds with functional kinds that are characterized exclusively in terms of causes and effects, abstracts from the physico-chemical level of microphysics and hence seemed to be a more suitable alternative explanation of the relation between mind and body. In fact, there are many functional kinds, such as mousetraps, software and bookshelves, which are multiply realized at the physical level.

Machine state functionalism

The first formulation of such a functionalist theory was put forth by Putnam himself. This formulation, which is now called machine-state functionalism, was inspired by the analogies which Putnam and others noted between the mind and the theoretical "machines" or computers capable of computing any given algorithm which were developed by Alan Turing (called universal Turing machines).

In non-technical terms, a Turing machine can be visualized as an infinitely long tape divided into squares (the memory) with a box-shaped scanning device that sits over and scans one square of the memory at a time. Each square is either blank (B) or has a 1 written on it. These are the inputs to the machine. The possible outputs are:

Halt: Do nothing.
R: move one square to the right.
L: move one square to the left.
B: erase whatever is on the square.
1: erase whatever is on the square and print a '1''.

An extremely simple example of a Turing machine which writes out the sequence '111' after scanning three blank squares and then stops is specified by the following machine table:

	State One	State Two	State Three
B	write 1; stay in state 1	write 1; stay in state 2	write 1; stay in state 3
1	go right; go to state 2	go right; go to state 3	^*

This table states that if the machine is in state one and scans a blank square (B), it will print a 1 and remain in state one. If it is in state one and reads a 1, it will move one square to the right and also go into state two. If it is in state two and reads a B, it will print a 1 and stay in state two. If it's in state two and reads a 1, it will move one square to the right and go into state three. Finally, if it is in state three and reads a B, it prints a 1 and remains in state three.

The essential point to consider here is the nature of the states of the Turing machine. Each state can be defined exclusively in terms of its relations to the other states as well as inputs and outputs. State one, for example, is simply the state in which the machine, if it reads a B, writes a 1 and stays in that state, and in which, if it reads a 1, it moves one square to the right and goes into a different state. This is the functional definition of state one; it is its causal role in the overall system. The details of how it accomplishes what it accomplishes and of its material constitution are completely irrelevant.

According to machine-state functionalism, the nature of a mental state is just like the nature of the automaton states described above. Just as state one simply is the state in which, given an input B, such and such happens, so being in pain is the state which disposes one to cry "ouch", become distracted, wonder what the cause is, and so forth.

Rejection of functionalism

In more recent years, Putnam has abandoned his adherence to functionalism and other forms of computational theories of the mind . This is primarily due to the enormous difficulties which such theories have in dealing with intuitions about the externalism of mental content as illustrated through Putnam's own Twin Earth thought experiment (see philosophy of language).

He also developed a separate argument in 1988, based on Fodor's generalized version of multiple realizability, against functionalism. Noting that functionalism is essentially a watered-down reductionist or identity theory in which mental kinds are ultimately identified with functional kinds, Putnam argued that mental kinds were probably multiply realizable over functional kinds. The same mental state or property could be implemented or realized by different states of a universal Turing machine.

Philosophy of language

Semantic externalism

One of Putnam's most significant contributions to the philosophy of language is his doctrine that "meaning just ain't in the head", which is most famously illustrated by his Twin Earth thought experiment. Concisely, he argues that if you see a liquid and call it "water" and some alien twin of yours (identical down to the last detail) on an alien planet sees what appears to be an identical liquid and calls it water AND if it turns out it was really XYZ and not H₂O, then you and your double actually mean something different by water even though water has the same function for both of you. This led Putnam to adopt a version of semantic externalism with regard to meaning and well as mental content.

Theory of meaning

Along with Saul Kripke, Keith Donnellan and others, Putnam made important contributions to what is known as the causal theory of reference.

In particular, Putnam maintains in The Meaning of "Meaning" that the objects referred to by natural kind terms (such as tiger, water, tree, and so on) are the principle elements of the meaning of such terms. There is a linguistic division of labor (analogous to Adam Smith's economic division of labor) according to which such terms have their references fixed by the "experts" in the particular field of science to which the terms belongs. So, for example, the reference of the term lion is fixed by the community of zoologists, the reference of the term elm tree is fixed by the community of botanists, the reference of the term table salt is fixed as NaCl by chemists, and so on. These referents are considered rigid designators in the Kripkean sense and are then disseminated outward to the linguistic community at large.

Putnam then specifies "a normal form (or, rather, a type of normal form) for the description of the meaning" of every term in the language. Such a "normal form" consists in a finite sequence - or vector - whose components are:

the object to which the term refers (the object individuated by the chemical formula H₂O, for example)
a set of characteristic descriptions (called the stereotype) such as for example transparent, colorless, dehydrating, etc.
the semantic indicators which place the object into a general category (e.g., natural kind, liquid, etc.) and
the syntactic indicators (concrete noun, mass noun, etc.).

Such a normal form offers a description of the reference and use of an expression within a particular linguistic community, providing explicit conditions for its correct usage and making it possible to judge whether a single speaker attributes to the expression E the appropriate meaning, or whether the use of E has undergone a transformation within the community significant enough to determine a semantic change. It is legitimate, according to Putnam, to speak of a change in meaning of an expression only if the reference of the term has changed and not its stereotype. But since there is no possible algorithm which can determine which aspect, the stereotype or the reference, has changed in a particular instance, it is necessary to consider the usage of other expressions of the language. Since there is no limit, in principle, to the number of such expressions which must be considered, Putnam embraces a form of semantic holism.

Philosophy of mathematics

One of Putnam's important contributions to the philosophy of mathematics is the so-called Quine-Putnam indispensability argument for mathematical realism (or mathematical platonism). The argument is considered by some to be the most powerful and convincing argument in favor of the acceptance of the actual existence of abstract mathematical entities, such as numbers and sets. The form of the argument is extremely simple:

(a) We must have ontological commitments to all and only the entities that are indispensable to our best scientific theories.

(b)Mathemathical entities are indispensable to our best scientific theories.

Ergo, (c) We must have ontological commitments to mathematical entities.

The justification for the first premise is obviously the most controversial. Both Putnam and Quine invoke naturalism to justify the elimination of all non-scientific or supernatural entities, and hence to defend the only part of all and only in the first premise. The assertion that all entities quantified over in scientific theories, including numbers, should be accepted as real is justified through the invocation of confirmation holism. Since theories are not confirmed in an atomistic and piecemeal fashion but as a whole, there seems be no logical justification for excluding any of the entities postulated by well-confirmed theories. This puts the nominalist who wishes to exclude the existence of sets and non-Euclidean geometry but include the existence of quarks and other postulated but undetectable entities of physics, for example, in a very difficult position.

Putnam also held the view that in mathematics, as in physics and other empirical sciences, we don't use only strict logical proofs, but rather, while not doing this explicitly, we use "quasi-empirical" methods. That is, methods like verifying by many calculations that for no integer n > 2 do there exist positive integer values of x, y, and z such that xⁿ + yⁿ = zⁿ (Fermat's last theorem proved in 1993 by Andrew Wiles). Even if we treat such knowledge as more conjectural than a strictly proven theorem, we still make use of it in developing mathematical ideas that are based on it.

As a mathematician, Putnam has also contributed to the resolution of Hilbert's tenth problem in mathematics.

Computer science

In computer science, Putnam is known for the Davis-Putnam algorithm for the Boolean satisfiability problem, developed with Martin Davis.

Epistemology

Putnam has also made an argument that is regarded by some as a refutation of skepticism known as the "Brain in a Vat" argument. He argues that you cannot coherently state that you are a "brain in a vat" placed there by a " Mad Scientist" (an old science fiction cliché, as seen in Dark City, and also an allusion to Descartes' Evil Genius). This is because, as in the Twin Earth case, if you are indeed a "brain in a vat", whose every experience is received through wiring and other gadgetry created by the Mad Scientist, then your idea of a "brain" would not refer to a "real" brain, since you never saw one - you only, perhaps, saw something that looks like a brain, but it was only fed to you through the wiring. Similarly, your idea of a "vat" would not refer to a "real" vat. So, if, as a "brain in a vat", you say "I'm a brain in a vat", you actually mean to say "I'm a vat-brain in a vat-vat", which is incoherent. If, on the other hand, you are not a "brain in a vat", then saying you are is still incoherent, but this time because you actually mean the opposite. This is a form of epistemological externalism: where knowledge or justification depends on factors outside of the mind or intellect and is not simply determined internally.

Philosophy of science and ontology

In the latter part of the 1980's and 1990's, Putnam abandoned his longstanding defence of, what he came to call, metaphysical realism, the view that the categories and structures of the external world are both causally and ontologically independent of the conceptualizations of the human mind. Instead he adopted a rather different view which he called internal realism or pragmatic realism.

Internal realism is essentially the view that, though the world is indeed causally independent of the human mind, the structure of the world - its division into kinds, individuals and categories, - is a function of the human mind, and hence the world is not ontologically independent. The general idea is substantially influenced by Kant's idea of the dependence of our knowledge of the world on the categories of thought.

The problem with metaphysical realism, according to Putnam, is that it fails to explain the possibility of reference and truth. According to the metaphysical realist, our concepts and categories refer because they match up in some mysterious manner with the pre-structured categories, kinds and individuals that are inherent in the external world. But how is it possible that the world "carves up" into certain structures and categories, the mind carves up the world into its own categories and structures, and the two "carvings" perfectly coincide? The answer must be that the world does not come pre-structured but that structure must be imposed on it by the human mind and its conceptual schemes.

Political ideology

Although Putnam has not written as extensively on politics as on other matters, he has been involved in political movements in the United States. In the late 1960s and early 1970s, he was a very active opponent of American military intervention in Vietnam as well as a supporter of civil rights causes. After 1968 most of these efforts were directed through the Progressive Labor Party. At one point, Harvard University attempted to censure Putnam for his political activities which the university administration considered disruptive, but he succeeded in rallying large numbers of friends and supporters to defeat this attempt. It is not known exactly when or why Putnam severed his ties with the PLP, but by 1975 he had broken off contact with the organization. In 1997, at a meeting of former draft resistance activists at Arlington Street Church in Boston, Putnam described his involvement with the PLP as a mistake. He said he had at first been impressed with PLP's commitment to alliance-building and its willingness to attempt to organize from within the armed forces.

Major works

Philosophy of Mathematics: Selected Readings. Edited with Paul Benacerraf. Englewood Cliffs, N.J.: Prentice-Hall, 1964. 2nd ed., Cambridge: Cambridge University Press, 1983.
Philosophy of Logic. New York: Harper and Row, 1971. London: George Allen and Unwin, 1972.
Mathematics, Matter and Method. Philosophical Papers, vol. 1. Cambridge: Cambridge University Press, 1975. 2nd. ed., 1985.
Mind, Language and Reality. Philosophical Papers, vol. 2. Cambridge: Cambridge University Press, 1975.
Meaning and the Moral Sciences. London: Routledge and Kegan Paul, 1978.
Reason, Truth, and History. Cambridge: Cambridge University Press, 1981.
Realism and Reason. Philosophical Papers, vol. 3. Cambridge: Cambridge University Press, 1983.
Methodology, Epistemology, and Philosophy of Science: Essays in Honour of Wolfgang Stegmüller. Edited with Wilhelm K. Essler and Carl G. Hempel. Dordrecht: D. Reidel, 1983.
Epistemology, Methodology, and Philosophy of Science: Essays in Honour of Carl G. Hempel. Edited with Wilhelm K. Essler and Wolfgang Stegmüller. Dordrecht: D. Reidel, 1985.
The Many Faces of Realism. La Salle, Ill.: Open Court, 1987.
Representation and Reality. Cambridge, Mass.: MIT Press, 1988.
Realism with a Human Face. Edited by James Conant. Cambridge, Mass.: Harvard University Press, 1990.
Renewing Philosophy. Cambridge, Mass.: Harvard University Press, 1992.
Pursuits of Reason: Essays in Honor of Stanley Cavell. Edited with Ted Cohen and Paul Guyer. Lubbock: Texas Tech University Press, 1993.
Words and Life. Edited by James Conant. Cambridge, Mass.: Harvard University Press, 1994.
Pragmatism: An Open Question. Oxford: Blackwell, 1995.
The Threefold Cord: Mind, Body, and World. New York: Columbia University Press, 1999.
Enlightenment and Pragmatism. Assen: Koninklijke Van Gorcum, 2001. 48pp.
The Collapse of the Fact/Value Dichotomy and Other Essays. Cambridge, Mass.: Harvard University Press, 2002.
Ethics Without Ontology. Cambridge, Mass.: Harvard University Press, 2004.

Works about Putnam

P. Clark-B. Hale (eds.), "Reading Putnam", Blackwell, Cambridge (Massachusetts)-Oxford 1995.
C.S. Hill (ed.), "The Philosophy of Hilary Putnam", Fayetteville, Arkansas 1992.
M. Rudel, "Erkenntnistheorie und Pragmatik: Untersuchungen zu Richard Rorty und Hilary Putnam", Hamburg 1987.

External links

Philosopher Olaf L Müller's elaboration of the Brain in a Vat argument
The God Problem recording of a discussion with Alvin Plantinga on The Connection radio show.
Hilary Putnam's homepage at Harvard.
Putnam's draft resistance work
Harvard Crimson article on Putnam's criticism of Harvard administration; see also others: [http://www.thecrimson.com/article.aspx?ref=356297

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