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Hilary Whitehall Putnam (; July 31, 1926 – March 13, 2016) was an American philosopher, mathematician, computer scientist, and figure in analytic philosophy in the second half of the 20th century. He contributed to the studies of philosophy of mind, philosophy of language, philosophy of mathematics, and philosophy of science. Outside philosophy, Putnam contributed to mathematics and computer science. Together with Martin Davis he developed the Davis–Putnam algorithm for the Boolean satisfiability problem and he helped demonstrate the unsolvability of Hilbert's tenth problem.
Putnam applied equal scrutiny to his own philosophical positions as to those of others, subjecting each position to rigorous analysis until he exposed its flaws. As a result, he acquired a reputation for frequently changing his positions. In philosophy of mind, Putnam argued against the type physicalism of mental and physical states based on his hypothesis of the multiple realizability of Mental event, and for the concept of functionalism, an influential theory regarding the mind–body problem. Putnam also originated the computational theory of mind. In philosophy of language, along with Saul Kripke and others, he developed the causal theory of reference, and formulated an original theory of meaning, introducing the notion of semantic externalism based on a thought experiment called Twin Earth. (1995). 9780631199953, Blackwell. ISBN 9780631199953
In philosophy of mathematics, Putnam and W. V. O. Quine developed the Quine–Putnam indispensability argument, an argument for the reality of mathematical entities, later espousing the view that mathematics is not purely logical, but "quasi-empirical". 2nd ed., Cambridge: Cambridge University Press, 1983. In epistemology, Putnam criticized the "brain in a vat" thought experiment, which appears to provide a powerful argument for skepticism, by challenging its coherence. reprinted in (1999). 9780195118261, Oxford University Press. ISBN 9780195118261 In metaphysics, he originally espoused a position called metaphysical realism, but eventually became one of its most outspoken critics, first adopting a view he called "internal realism", which he later abandoned. Despite these changes of view, throughout his career Putnam remained committed to scientific realism, roughly the view that mature scientific theories are approximately true descriptions of ways things are.
In his later work, Putnam became increasingly interested in Pragmatism, Jewish philosophy, and ethics, engaging with a wider array of philosophical traditions. He also displayed an interest in metaphilosophy, seeking to "renew philosophy" from what he identified as narrow and inflated concerns. He was at times a politically controversial figure, especially for his involvement with the Progressive Labor Party in the late 1960s and early 1970s.
Putnam completed the first two years of his primary education in France before he and his parents returned to the U.S. in 1933, settling in Philadelphia. There, he attended Central High School, where he met Noam Chomsky, who was a year behind him. The two remained friends—and often intellectual opponents—for the rest of Putnam's life. Putnam studied philosophy at the University of Pennsylvania, receiving his B.A. degree and becoming a member of the Philomathean Society, the country's oldest continually existing collegiate literary society. He did graduate work in philosophy at Harvard University and later at UCLA's philosophy department, where he received his Ph.D. in 1951 for his dissertation, The Meaning of the Concept of Probability in Application to Finite Sequences. Putnam's dissertation supervisor Hans Reichenbach was a leading figure in logical positivism, the dominant school of philosophy of the day; one of Putnam's most consistent positions was his rejection of logical positivism as self-defeating. Over the course of his life, Putnam was his own philosophical adversary, changing his positions on philosophical questions and critiquing his previous views.
After obtaining his PhD, Putnam taught at Northwestern University (1951–52), Princeton University (1953–61), and MIT (1961–65). For the rest of his career, Putnam taught at Harvard's philosophy department, becoming Cogan University Professor. In 1962, he married fellow philosopher Ruth Anna Putnam (born Ruth Anna Jacobs), who took a teaching position in philosophy at Wellesley College. Rebelling against the antisemitism they experienced during their youth, the Putnams decided to establish a traditional Jewish home for their children. Since they had no experience with the rituals of Judaism, they sought out invitations to other Jewish homes for Passover Seder. They began to study Jewish rituals and Hebrew language, became more interested in Judaism, self-identified as Jews, and actively practiced Judaism. In 1994, Hilary celebrated a belated bar mitzvah service; Ruth Anna's bat mitzvah was celebrated four years later.
In the 1960s and early 1970s, Putnam was an active supporter of the American Civil Rights Movement and he was also an active opponent of the Vietnam War. In 1963, he organized one of MIT's first faculty and student anti-war committees. After moving to Harvard in 1965, he organized campus protests and began teaching courses on Marxism. Putnam became an official faculty advisor to the Students for a Democratic Society and in 1968 a member of the Progressive Labor Party (PLP). He was elected a Fellow of the American Academy of Arts and Sciences in 1965. After 1968, his political activities centered on the PLP. The Harvard administration considered these activities disruptive and attempted to censure Putnam. Putnam permanently severed his relationship with the PLP in 1972. In 1997, at a meeting of former draft resistance activists at Boston's Arlington Street Church, he called his involvement with the PLP a mistake. He said he had been impressed at first with the PLP's commitment to alliance-building and its willingness to attempt to organize from within the armed forces.
In 1976, Putnam was elected president of the American Philosophical Association. The next year, he was selected as Walter Beverly Pearson Professor of Mathematical Logic in recognition of his contributions to the philosophy of logic and mathematics. While breaking with his radical past, Putnam never abandoned his belief that academics have a particular social and ethical responsibility toward society. He continued to be forthright and progressive in his political views, as expressed in the articles "How Not to Solve Ethical Problems" (1983) and "Education for Democracy" (1993).
Putnam was a Corresponding Fellow of the British Academy. He was elected to the American Philosophical Society in 1999. He retired from teaching in June 2000, becoming Cogan University Professor Emeritus, but as of 2009 continued to give a seminar almost yearly at Tel Aviv University. He also held the Spinoza Chair of Philosophy at the University of Amsterdam in 2001. His corpus includes five volumes of collected works, seven books, and more than 200 articles. Putnam's renewed interest in Judaism inspired him to publish several books and essays on the topic. With his wife, he co-authored several essays and a book on the late-19th-century American pragmatism movement.
For his contributions in philosophy and logic, Putnam was awarded the Rolf Schock Prize in 2011 and the Nicholas Rescher Prize for Systematic Philosophy in 2015. Putnam died at his home in Arlington, Massachusetts, on March 13, 2016. At the time of his death, Putnam was Cogan University Professor Emeritus at Harvard University.
Putnam also formulated an a priori argument in favor of multiple realizability 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'." In the case of computers, two machines are functionally isomorphic if and only if the sequential relations among states in the first exactly mirror the sequential relations among states in the other. Therefore, a computer made of silicon chips and one made of cogs and wheels can be functionally isomorphic but constitutionally diverse. Functional isomorphism implies multiple realizability.
Putnam, Jerry Fodor, and others argued that along with being an effective argument against type-identity theories, multiple realizability implies that any low-level explanation of higher-level mental phenomena is insufficiently abstract and general. Functionalism, which identifies mental kinds with functional kinds that are characterized exclusively in terms of causes and effects, abstracts from the level of microphysics, and therefore seemed to be a better explanation of the relation between mind and body. In fact, there are many functional kinds, including mousetraps and eyes, that are multiply realized at the physical level.
Multiple realizability has been criticized on the grounds that, if it were true, research and experimentation in the neurosciences would be impossible. According to William Bechtel and Jennifer Mundale, to be able to conduct such research in the neurosciences, universal consistencies must either exist or be assumed to exist in brain structures. It is the similarity (or homology) of brain structures that allows us to generalize across species. If multiple realizability were an empirical fact, results from experiments conducted on one species of animal (or one organism) would not be meaningful when generalized to explain the behavior of another species (or organism of the same species). Jaegwon Kim, David Lewis, Robert Richardson and Patricia Churchland have also criticized metaphysical realism.
Putnam's change of mind was primarily due to the difficulties computational theories have in explaining certain intuitions with respect to the externalism of mental content. This is illustrated by his Twin Earth thought experiment.Rescorla, M., "The Computational Theory of Mind", esp. 5.2 Externalism about mental content, Stanford Encyclopedia of Philosophy, December 18, 2024.
In 1988 Putnam also developed a separate argument against functionalism based on Fodor's generalized version of multiple realizability. Asserting that functionalism is really a watered-down identity theory in which mental kinds are identified with functional kinds, he argued that mental kinds may be multiply realizable over functional kinds. The argument for functionalism is that the same mental state could be implemented by the different states of a universal Turing machine.Stillings, N. A., Cognitive Science: An Introduction (Cambridge, MA: The MIT Press, 1995), p. 347.
Despite Putnam's rejection of functionalism, it has continued to flourish and been developed into numerous versions by Fodor, David Marr, Daniel Dennett, and David Lewis, among others. Functionalism helped lay the foundations for modern cognitive science and was the dominant theory of mind in philosophy in the last part of the 20th century.
By 2012 Putnam accepted a modification of functionalism called "liberal functionalism". The view holds that "what matters for consciousness and for mental properties generally is the right sort of functional capacities and not the particular matter that subserves those capacities". The specification of these capacities may refer to what goes on outside the organism's "brain", may include intentional idioms, and need not describe a capacity to compute something or other.
Putnam himself formulated one of the main arguments against functionalism, the Twin Earth thought experiment, though there have been additional criticisms. John Searle's Chinese room argument (1980) is a direct attack on the claim that thought can be represented as a set of functions. It is designed to show that it is possible to mimic intelligent action with a purely functional system, without any interpretation or understanding. Searle describes a situation in which a person who speaks only English is locked in a room with Chinese symbols in baskets and a rule book in English for moving the symbols around. People outside the room instruct the person inside to follow the rule book for sending certain symbols out of the room when given certain symbols. The people outside the room speak Chinese and are communicating with the person inside via the Chinese symbols. According to Searle, it would be absurd to claim that the English speaker inside "knows" Chinese based on these syntactic processes alone. This argument attempts to show that systems that operate merely on syntactic processes cannot realize any semantics (meaning) or intentionality (aboutness). Searle thus attacks the idea that thought can be equated with following a set of syntactic rules and concludes that functionalism is an inadequate theory of the mind. Ned Block has advanced several other arguments against functionalism.
Twin Earth shows this, according to Putnam, since on Twin Earth everything is identical to Earth, except that its lakes, rivers and oceans are filled with XYZ rather than H2O. Consequently, when an earthling, Fredrick, uses the Earth-English word "water", it has a different meaning from the Twin Earth-English word "water" when used by his physically identical twin, Frodrick, on Twin Earth. Since Fredrick and Frodrick are physically indistinguishable when they utter their respective words, and since their words have different meanings, meaning cannot be determined solely by what is in their heads. This led Putnam to adopt a version of semantic externalism with regard to meaning and mental content. The philosopher of mind and language Donald Davidson, despite his many differences of opinion with Putnam, wrote that semantic externalism constituted an "anti-subjectivist revolution" in philosophers' way of seeing the world. Since Descartes's time, philosophers had been concerned with proving knowledge from the basis of subjective experience. Thanks to Putnam, Saul Kripke, Tyler Burge and others, Davidson said, philosophy could now take the objective realm for granted and start questioning the alleged "truths" of subjective experience.
Putnam specifies a finite sequence of elements (a vector) for the description of the meaning of every term in the language. Such a vector consists of four components:
Such a "meaning-vector" provides a description of the reference and use of an expression within a particular linguistic community. It provides the conditions for its correct usage and makes it possible to judge whether a single speaker attributes the appropriate meaning to it or whether its use has changed enough to cause a difference in its meaning. According to Putnam, it is legitimate to speak of a change in the meaning of an expression only if the reference of the term, and not its stereotype, has changed. But since no possible algorithm can determine which aspect—the stereotype or the reference—has changed in a particular case, it is necessary to consider the usage of other expressions of the language. Since there is no limit to the number of such expressions to be considered, Putnam embraced a form of semantic holism. (2026). 9788886570855, Quodlibet. ISBN 9788886570855
Despite the many changes in his other positions, Putnam consistently adhered to semantic holism. Michael Dummett, Jerry Fodor, Ernest Lepore, and others have identified problems with this position. In the first place, they suggest that, if semantic holism is true, it is impossible to understand how a speaker of a language can learn the meaning of an expression in the language. Given the limits of our cognitive abilities, we will never be able to master the whole of the English (or any other) language, even based on the (false) assumption that languages are static and immutable entities. Thus, if one must understand all of a natural language to understand a single word or expression, language learning is simply impossible. Semantic holism also fails to explain how two speakers can mean the same thing when using the same expression, and therefore how any communication is possible between them. Given a sentence P, since Fred and Mary have each mastered different parts of the English language and P is related in different ways to the sentences in each part, P means one thing to Fred and something else to Mary. Moreover, if P derives its meaning from its relations with all the sentences of a language, as soon as the vocabulary of an individual changes by the addition or elimination of a sentence, the totality of relations changes, and therefore also the meaning of P. As this is a common phenomenon, the result is that P has two different meanings in two different moments in the life of the same person. Consequently, if one accepts the truth of a sentence and then rejects it later on, the meaning of what one rejected and what one accepted are completely different and therefore one cannot change opinions with regard to the same sentences. (1992). 9780631181927, Blackwell. ISBN 9780631181927
In 1975, Putnam formulated his own indispensability argument based on the no miracles argument in the philosophy of science, saying, "I believe that the positive argument for realism in has an analogue in the case of mathematical realism. Here too, I believe, realism is the only philosophy that doesn't make the success of the science a miracle". According to Putnam, Quine's version of the argument was an argument for the existence of abstract mathematical objects, while Putnam's own argument was simply for a realist interpretation of mathematics, which he believed could be provided by a "mathematics as modal logic" interpretation that need not imply the existence of abstract objects.
Putnam also held the view that mathematics, like physics and other empirical sciences, uses both strict logical proofs and "quasi-empirical" methods. (2026). 9783319962733, Springer. ISBN 9783319962733 For example, Fermat's Last Theorem states that for no integer are there positive integer values of x, y, and z such that . Before Andrew Wiles proved this for all in 1995, it had been proved for many values of n. These proofs inspired further research in the area, and formed a quasi-empirical consensus for the theorem. Even though such knowledge is more conjectural than a strictly proved theorem, it was still used in developing other mathematical ideas.
The Quine–Putnam indispensability argument has been extremely influential in the philosophy of mathematics, inspiring continued debate and development of the argument in contemporary philosophy of mathematics. According to the Stanford Encyclopedia of Philosophy, many in the field consider it the best argument for mathematical realism. Prominent counterarguments come from Hartry Field, who argues that mathematics is not indispensable to science, and Penelope Maddy and Elliott Sober, who dispute whether we are committed to mathematical realism even if it is indispensable to science.
In computability theory, Putnam investigated the structure of the ramified analytical hierarchy, its connection with the constructible hierarchy and its . He showed that there are many levels of the constructible hierarchy that add no subsets of the integers. Later, with his student George Boolos, he showed that the first such "non-index" is the ordinal of ramified analysis (this is the smallest such that is a model of full second-order comprehension). Also, together with a separate paper with his student Richard Boyd and Gustav Hensel, he demonstrated how the Davis–Mostowski–Kleene hyperarithmetical hierarchy of arithmetical degrees can be naturally extended up to .
In computer science, Putnam is known for the Davis–Putnam algorithm for the Boolean satisfiability problem (SAT), developed with Martin Davis in 1960. The algorithm finds whether there is a set of true or false values that satisfies a given Boolean expression so that the entire expression becomes true. In 1962, they further refined the algorithm with the help of George Logemann and Donald W. Loveland. It became known as the DPLL algorithm. It is efficient and still forms the basis of most complete SAT solvers.
This follows from the causal theory of reference. Words always refer to the kinds of things they were coined to refer to, the kinds of things their user, or the user's ancestors, experienced. So, if some person, Mary, is a "brain in a vat", whose every experience is received through wiring and other gadgetry created by the mad scientist, then Mary's idea of a brain does not refer to a real brain, since she and her linguistic community have never encountered such a thing. To her a brain is actually an image fed to her through the wiring. Nor does her idea of a vat refer to a real vat. So if, as a brain in a vat, she says, "I'm a brain in a vat", she is actually saying, "I'm a brain-image in a vat-image", which is incoherent. On the other hand, if she is not a brain in a vat, then saying that she is a brain in a vat is still incoherent, because she actually means the opposite. This is a form of epistemological externalism: knowledge or justification depends on factors outside the mind and is not solely determined internally.
Putnam has clarified that his real target in this argument was never skepticism, but metaphysical realism, which he thought implied such skeptical scenarios were possible. Since realism of this kind assumes the existence of a gap between how one conceives the world and the way the world really is, skeptical scenarios such as this one (or Descartes's evil demon) present a formidable challenge. By arguing that such a scenario is impossible, Putnam attempts to show that this notion of a gap between one's concept of the world and the way it is is absurd. One cannot have a "God's-eye" view of reality. One is limited to one's conceptual schemes, and metaphysical realism is therefore false.
Putnam's brain in a vat argument has been criticized. Crispin Wright argues that Putnam's formulation of the brain-in-a-vat scenario is too narrow to refute global skepticism. The possibility that one is a recently disembodied brain in a vat is not undermined by semantic externalism. If a person has lived their entire life outside the vat—speaking the English language and interacting normally with the outside world—before "envatment" by a mad scientist, when they wake up inside the vat, their words and thoughts (e.g., "tree" and "grass") will still refer to the objects or events in the external world they had referred to before envatment.
According to Putnam, the problem with metaphysical realism 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 categories, kinds and individuals 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 the human mind and its conceptual schemes impose structure on it. In Reason, Truth, and History, Putnam identified truth with what he termed "idealized rational acceptability." The theory is that a belief is true if it would be accepted by anyone under ideal epistemic conditions.
Nelson Goodman formulated a similar notion in Fact, Fiction and Forecast (1956). "We have come to think of the actual as one among many possible worlds. We need to repaint that picture. All possible worlds lie within the actual one", Goodman wrote. Putnam rejected this form of social constructivism, but retained the idea that there can be many correct descriptions of reality. None of these descriptions can be scientifically proven to be the "one, true" description of the world. He thus accepted "conceptual relativity"—the view that it may be a matter of choice or convention, e.g., whether sums exist, or whether spacetime points are individuals or mere limits.
Curtis Brown has criticized Putnam's internal realism as a disguised form of subjective idealism, in which case it is subject to the traditional arguments against that position. In particular, it falls into the trap of solipsism. That is, if existence depends on experience, as subjective idealism maintains, and if one's consciousness ceased to exist, then the rest of the universe would also cease to exist. In his reply to Simon Blackburn in the volume Reading Putnam, Putnam renounced internal realism because it assumed a "cognitive interface" model of the relation between the mind and the world. Under the increasing influence of William James and the pragmatism, he adopted a direct realist view of this relation. Although he abandoned internal realism, Putnam still resisted the idea that any given thing or system of things can be described in exactly one complete and correct way. He came to accept metaphysical realism in a broader sense, rejecting all forms of verificationism and all talk of our "making" the world.
In the philosophy of perception, Putnam came to endorse direct realism, according to which perceptual experiences directly present one with the external world. He once further held that there are no mental representations, sense data, or other intermediaries between the mind and the world. By 2012, however, he rejected this commitment in favor of "transactionalism", a view that accepts both that perceptual experiences are world-involving transactions, and that these transactions are functionally describable (provided that worldly items and intentional states may be referred to in the specification of the function). Such transactions can further involve qualia.
Many of Putnam's last works addressed the concerns of ordinary people, particularly social problems. For example, he wrote about the nature of democracy, social justice and religion. He also discussed Jürgen Habermas's ideas, and wrote articles influenced by continental philosophy.
An exhaustive bibliography of Putnam's writings, compiled by John R. Shook, can be found in The Philosophy Of Hilary Putnam (2015).
Metaphilosophy and ontology
In the late 1970s and the 1980s, stimulated by results from mathematical logic and by some of Quine's ideas, Putnam abandoned his long-standing defense of 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—and adopted a rather different view, which he called " internal realism" or " pragmatic realism". Internal realism is the view that, although the world may be causally independent of the human mind, the world's structure—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 influenced by Immanuel Kant's idea of the dependence of our knowledge of the world on the categories of thought.
Quantum mechanics
During his career, Putnam espoused various positions on the interpretation of quantum mechanics. In the 1960s and 1970s, he contributed to the quantum logic tradition, holding that the way to resolve quantum theory's apparent paradoxes is to modify the logical rules by which propositions' truth values are deduced. Putnam's first foray into this topic was "A Philosopher Looks at Quantum Mechanics" in 1965, followed by his 1969 essay "Is Logic Empirical?". He advanced different versions of quantum logic over the years, and eventually turned away from it in the 1990s, due to critiques by Nancy Cartwright, Michael Redhead, and others. In 2005, he wrote that he rejected the many-worlds interpretation because he could see no way for it to yield meaningful probabilities. He found both de Broglie–Bohm theory and the spontaneous collapse theory of Ghirardi, Rimini, and Weber to be promising, yet also dissatisfying, since it was not clear that either could be made fully consistent with special relativity's symmetry requirements.
Neopragmatism and Wittgenstein
In the mid-1970s, Putnam became increasingly disillusioned with what he perceived as modern analytic philosophy's "scientism" and focus on metaphysics over ethics and everyday concerns.R. M. de Gaynesford (2026). 9781844650408, McGill–Queen's University Press / Acumen. ISBN 9781844650408 He also became convinced by his readings of James and John Dewey that there is no fact–value dichotomy; that is, normative (e.g., ethical and aesthetic) judgments often have a factual basis, while scientific judgments have a normative element. For a time, under Ludwig Wittgenstein's influence, Putnam adopted a pluralist view of philosophy itself and came to view most philosophical problems as no more than conceptual or linguistic confusions philosophers created by using ordinary language out of context. A book of articles on pragmatism by Ruth Anna Putnam and Hilary Putnam, Pragmatism as a Way of Life: The Lasting Legacy of William James and John Dewey, edited by David Macarthur, was published in 2017.
Legacy
Recognition
Philosopher Martha Nussbaum called Putnam one of the greatest philosophers ever produced by America and compared him to Aristotle in that both made prolific contributions to a wide range of topics, even noting that Putnam added to a couple of areas Aristotle did not. The linguist and activist Noam Chomsky stated that "he had enormous talents and creativity, one of the finest minds I've ever encountered." Philosopher Warren Goldfarb stated "I don't know anyone else who had his breadth or so quickly assimilated things in all different areas. He was essentially the quickest mind I've ever encountered."
Works
Books authored
(1993). 089672266X, Texas Tech University Press. 089672266X
H. Putnam (1995). 063119343X, Blackwell. 063119343X Based on the Gifford Lectures that Putnam delivered at the University of St Andrews in 1990 and 1991.
Books edited
(1983). 9789027716460, D. Reidel. ISBN 9789027716460
Select papers, book chapters and essays
See also
Further reading
(2026). 9783110769166, De Gruyter. ISBN 9783110769166
External links
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