David Lewis (philosopher)

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David Lewis
David Kellogg Lewis

September 28, 1941
DiedOctober 14, 2001 (aged 60)
Other namesBruce Le Catt [1]
Alma mater Swarthmore College
Oxford University
Harvard University
Era 20th-century philosophy
Region Western philosophy
School Analytic
Nominalism [2]
Perdurantism [3]
Doctoral advisor Willard Van Orman Quine
Other academic advisors Donald Cary Williams [4]
Doctoral students Robert Brandom
J. David Velleman
Main interests
Logic  · Language  · Metaphysics
Epistemology  · Ethics
Notable ideas
Possible worlds  · Modal realism  · Counterfactuals  · Counterpart theory  · Principal principle  · Humean supervenience  · Lewis signaling game  ·The endurantismperdurantism distinction
Descriptive-causal theory of reference [5]  · De se
Qualitative vs quantitative parsimony [6]
Ramsey–Lewis method
Gunk [7]
Ontological innocence [8]

David Kellogg Lewis (September 28, 1941 – October 14, 2001) was an American philosopher. Lewis taught briefly at UCLA and then at Princeton from 1970 until his death. He is also closely associated with Australia, whose philosophical community he visited almost annually for more than thirty years. He made contributions in philosophy of language, philosophy of mind, philosophy of probability, metaphysics, epistemology, philosophical logic, and aesthetics. He is probably best known for his controversial modal realist stance:
(i) Possible worlds exist.
(ii) Every possible world is a concrete entity.
(iii) Any possible world is causally and spatiotemporally isolated from any other possible world.
(iv) Our world is among the possible worlds.

Princeton University University in Princeton, New Jersey

Princeton University is a private Ivy League research university in Princeton, New Jersey. Founded in 1746 in Elizabeth as the College of New Jersey, Princeton is the fourth-oldest institution of higher education in the United States and one of the nine colonial colleges chartered before the American Revolution. The institution moved to Newark in 1747, then to the current site nine years later, and renamed itself Princeton University in 1896.

Australia Country in Oceania

Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania and numerous smaller islands. It is the largest country in Oceania and the world's sixth-largest country by total area. The neighbouring countries are Papua New Guinea, Indonesia and East Timor to the north; the Solomon Islands and Vanuatu to the north-east; and New Zealand to the south-east. The population of 25 million is highly urbanised and heavily concentrated on the eastern seaboard. Australia's capital is Canberra, and its largest city is Sydney. The country's other major metropolitan areas are Melbourne, Brisbane, Perth and Adelaide.

Philosophy of language, in the analytical tradition, explored logic, the nature of meaning, and accounts of the mind.


Early life and education

Lewis was born in Oberlin, Ohio, to John D. Lewis, a Professor of Government at Oberlin College, and Ruth Ewart Kelloggs Lewis, a distinguished medieval historian. The formidable intellect for which he was known later in his life was already manifest during his years at Oberlin High School, when he attended college lectures in chemistry. He went on to Swarthmore College and spent a year at Oxford University (1959–1960), where he was tutored by Iris Murdoch and attended lectures by Gilbert Ryle, H.P. Grice, P.F. Strawson, and J.L. Austin. It was his year at Oxford that played a seminal role in his decision to study philosophy, and which made him the quintessentially analytic philosopher that he would soon become. Lewis went on to receive his Ph.D from Harvard in 1967, where he studied under W.V.O. Quine, many of whose views he came to repudiate. It was there that his connection with Australia was first established when he took a seminar with J.J.C. Smart, a leading Australian philosopher. "I taught David Lewis," Smart would say in later years, "Or rather, he taught me."

Oberlin, Ohio City in Ohio, United States

Oberlin is a city in Lorain County, Ohio, United States, southwest of Cleveland. Oberlin is the home of Oberlin College, a liberal arts college and music conservatory with approximately 3,000 students.

Ohio State of the United States of America

Ohio is a Midwestern state in the Great Lakes region of the United States. Of the fifty states, it is the 34th largest by area, the seventh most populous, and the tenth most densely populated. The state's capital and largest city is Columbus.

Oberlin College Private liberal arts college in Oberlin, Ohio, United States

Oberlin College is a private liberal arts college in Oberlin, Ohio. It is the oldest coeducational liberal arts college in the United States and the second oldest continuously operating coeducational institute of higher learning in the world. The Oberlin Conservatory of Music is the oldest continuously operating conservatory in the United States. In 1835 Oberlin became one of the first colleges in the United States to admit African Americans, and in 1837 the first to admit women.

Early work on convention

Lewis's first monograph was Convention: A Philosophical Study (1969), which is based on his doctoral dissertation and uses concepts of game theory to analyze the nature of social conventions; it won the American Philosophical Association's first Franklin Matchette Prize for the best book published in philosophy by a philosopher under 40 years old. Lewis claimed that social conventions, such as the convention in most states that one drives on the right (not on the left), the convention that the original caller will re-call if a phone conversation is interrupted, etc., are solutions to so-called "'co-ordination problems'". Co-ordination problems were at the time of Lewis's book an under-discussed kind of game-theoretical problem; most of the game-theoretical discussion had circulated around problems where the participants are in conflict, such as the prisoner's dilemma.

Game theory is the study of mathematical models of strategic interaction between rational decision-makers. It has applications in all fields of social science, as well as in logic and computer science. Originally, it addressed zero-sum games, in which one person's gains result in losses for the other participants. Today, game theory applies to a wide range of behavioral relations, and is now an umbrella term for the science of logical decision making in humans, animals, and computers.

The American Philosophical Association (APA) is the main professional organization for philosophers in the United States. Founded in 1900, its mission is to promote the exchange of ideas among philosophers, to encourage creative and scholarly activity in philosophy, to facilitate the professional work and teaching of philosophers, and to represent philosophy as a discipline.

The prisoner's dilemma is a standard example of a game analyzed in game theory that shows why two completely rational individuals might not cooperate, even if it appears that it is in their best interests to do so. It was originally framed by Merrill Flood and Melvin Dresher while working at RAND in 1950. Albert W. Tucker formalized the game with prison sentence rewards and named it "prisoner's dilemma", presenting it as follows:

Two members of a criminal gang are arrested and imprisoned. Each prisoner is in solitary confinement with no means of communicating with the other. The prosecutors lack sufficient evidence to convict the pair on the principal charge, but they have enough to convict both on a lesser charge. Simultaneously, the prosecutors offer each prisoner a bargain. Each prisoner is given the opportunity either to betray the other by testifying that the other committed the crime, or to cooperate with the other by remaining silent. The offer is:

Co-ordination problems are problematic, for, though the participants have common interests, there are several solutions. Sometimes, one of the solutions may be "'salient'", a concept invented by the game-theorist and economist Thomas Schelling (by whom Lewis was much inspired). For example, a co-ordination problem that has the form of a meeting may have a salient solution if there is only one possible spot to meet in town. But in most cases, we must rely on what Lewis calls "precedent" in order to get a salient solution. If both participants know that a particular co-ordination problem, say "which side should we drive on?" has been solved in the same way numerous times before, both know that both know this, both know that both know that both know this, etc. (this particular state Lewis calls common knowledge, and it has since been much discussed by philosophers and game theorists), then they will easily solve the problem. That they have solved the problem successfully will be seen by even more people, and thus the convention will spread in the society. A convention is thus a behavioural regularity that sustains itself because it serves the interests of everyone involved. Another important feature of a convention is that a convention could be entirely different: one could just as well drive on the left; it is more or less arbitrary that one drives on the right in the US, for example.

Thomas Schelling American economist

Thomas Crombie Schelling was an American economist and professor of foreign policy, national security, nuclear strategy, and arms control at the School of Public Policy at University of Maryland, College Park. He was also co-faculty at the New England Complex Systems Institute. He was awarded the 2005 Nobel Memorial Prize in Economic Sciences for "having enhanced our understanding of conflict and cooperation through game-theory analysis."

Common knowledge is a special kind of knowledge for a group of agents. There is common knowledge of p in a group of agents G when all the agents in G know p, they all know that they know p, they all know that they all know that they know p, and so on ad infinitum.

Lewis's main goal in the book, however, wasn't simply to provide an account of convention but rather to investigate the "platitude that language is ruled by convention" (Convention, p. 1.) The last two chapters of the book (Signalling Systems and Conventions of Language; cf. also "Languages and Language", 1975) make the case that the use of a language in a population consists of conventions of truthfulness and trust among members of the population. Lewis recasts in this framework notions such as those of truth and analyticity, claiming that they are better understood as relations between sentences and a language, rather than as properties of sentences.

Counterfactuals and modal realism

Lewis went on to publish Counterfactuals (1973), which contained an analysis of counterfactual conditionals in terms of the theory of possible worlds. According to Lewis, what makes a statement of the form

Had I made that shot our team would have won the game.

true is that in any world where I make the shot but the world is otherwise as similar as possible to the actual one, our team wins the game. If there is a world maximally similar to ours where I make the shot but our team still loses, the counterfactual is false. This treatment of counterfactuals is a variation or generalization of the one published by Robert Stalnaker a few years earlier, and consequently this kind of treatment is called the Stalnaker-Lewis theory.

Robert C. Stalnaker is an American philosopher, who is Laurence S. Rockefeller Professor of Philosophy at the Massachusetts Institute of Technology. He is a Fellow of the American Academy of Arts and Sciences and a Corresponding Fellow of the British Academy.

Realism about possible worlds

What made Lewis's views about counterfactuals controversial is that whereas Stalnaker treated possible worlds as imaginary entities, "made up" for the sake of theoretical convenience, Lewis adopted a position his formal account of counterfactuals did not commit him to, namely modal realism. According to this view as Lewis formulated it, when we speak of a world where I made the shot that in this world I missed, we are speaking of a world just as real as this one, and although we say that in that world I made the shot, more precisely it is not I but a counterpart of mine that was successful.

He had already proposed this view in some of his earlier papers: "Counterpart Theory and Quantified Modal Logic" (1968), "Anselm and Actuality" (1970), and "Counterparts of Persons and their Bodies" (1971). The theory was widely considered implausible, but Lewis urged that it should be taken seriously. Most often the idea that there exists an infinite number of causally isolated universes, each as real as our own but different from it in some way, and that furthermore that alluding to objects in this universe as necessary in order to explain what makes certain counterfactual statements true but not others, meets with what Lewis calls the "incredulous stare" (Lewis, OPW, 2005, pg. 135–137). Lewis defends and elaborates his theory of extreme modal realism, while insisting that there is nothing extreme about it, in On the Plurality of Worlds (1986). Lewis acknowledges that his theory is contrary to common sense, but believes that its advantages far outweigh this disadvantage, and that therefore we should not be hesitant to pay this price.

According to Lewis, "actual" is merely an indexical label we give to a world when we locate ourselves in it. Things are necessarily true when they are true in all possible worlds. (Note that Lewis is not the first one to speak of possible worlds in this context. Leibniz and C.I. Lewis, for example, both speak of possible worlds as a way of thinking about possibility and necessity, and some of David Kaplan's early work is on the counterpart theory. Lewis's original suggestion was that all possible worlds are equally concrete, and the world in which we find ourselves is no more real than any other possible world.)


This theory has faced a number of criticisms. In particular, it is not clear how we could know what goes on in other worlds. After all, they are causally disconnected from ours; we can't look into them to see what is going on there. [10] A related objection is that, while people are concerned with what they could have done, they are not concerned with what some people in other worlds, no matter how similar to them, do. As Saul Kripke once put it, a presidential candidate could not care less whether someone else, in another world, wins an election, but does care whether he himself could have won it (Kripke 1980, p. 45). A more basic criticism is that introducing so many entities into our ontology violates the maxim of Occam's razor, which tells us not to multiply theoretical entities beyond what is necessary to explain the facts our theories aim to explain.

Possible worlds are employed in the work of Saul Kripke [11] and many others, but not in the concrete sense propounded by Lewis. While none of these alternative approaches has found anything near universal acceptance, very few philosophers accept Lewis's particular brand of modal realism.


At Princeton, Lewis was a mentor of young philosophers, and trained dozens of successful figures in the field, including several current Princeton faculty members, as well as people now teaching at a number of the leading philosophy departments in the U.S. Among his most prominent students are Bob Brandom at the University of Pittsburgh, L.A. Paul at the University of North Carolina, Cian Dorr and David Velleman at NYU, Peter Railton at Michigan, and Joshua Greene at Harvard. His direct and indirect influence is evident in the work of many prominent philosophers of the current generation.

Later life and death

Lewis suffered from severe diabetes for much of his life, which eventually grew worse and led to kidney failure. In July 2000 he received a kidney transplant from his wife Stephanie. The transplant allowed him to work and travel for another year, before he died suddenly and unexpectedly from further complications of his diabetes, on October 14, 2001. [12]

Since his death a number of posthumous papers have been published, on topics ranging from truth and causation to philosophy of physics. Lewisian Themes, a collection of papers on his philosophy, was published in 2004.



Lewis published five volumes containing 99 papers — almost all of the papers he published during his lifetime. These papers discuss his counterfactual theory of causation, the concept of semantic score, a contextualist analysis of knowledge, a dispositional value theory, among many other topics.

Lewis's monograph, Parts of Classes (1991), on the foundations of mathematics, sketched a reduction of set theory and Peano arithmetic to mereology and plural quantification. Very soon after its publication, Lewis became dissatisfied with some aspects of its argument; it is currently out of print (his paper "Mathematics is megethology," in "Papers in Philosophical Logic," is partly a summary and partly a revision of "Parts of Classes").

Selected papers

See also

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  1. Guglielmi, Giorgia (1 August 2017). "Philosophy journal corrects 35-year-old article 'written' by a cat". Science .
  2. "Review of Gonzalo Rodriguez-Pereyra, Resemblance Nominalism: A Solution to the Problem of Universals" – ndpr.nd.edu
  3. Lewis, D. K. 1986. On the Plurality of Worlds Oxford: Blackwell.
  4. Wolterstorff, Nicholas (November 2007). "A Life in Philosophy". Proceedings and Addresses of the American Philosophical Association. 81 (2): 93–106. JSTOR   27653995.
  5. Stefano Gattei, Thomas Kuhn's 'Linguistic Turn' and the Legacy of Logical Empiricism: Incommensurability, Rationality and the Search for Truth, Ashgate Publishing, 2012, p. 122 n. 232.
  6. "On Quantitative and Qualitative Parsimony" by Maciej Sendłak, Metaphilosophy49(1–2):153–166 (2018).
  7. "David Lewis's Metaphysics"
  8. "An Argument for the Ontological Innocence of Mereology"
  9. Stathis Psillos, Scientific Realism: How Science Tracks Truth, Routledge, 1999, p. xxiii.
  10. Stalnaker, Inquiry, p. 49: "But if other possible worlds are causally disconnected from us, how do we know anything about them?"
  11. "Naming and Necessity", In Semantics of Natural Language, edited by D. Davidson and G. Harman. 1980 (1972) Dordrecht; Boston: Reidel.
  12. "David Kellogg Lewis". The New York Times . October 20, 2001. David Kellogg Lewis, a metaphysician and a philosopher of mind, language and logic at Princeton University, died on Sunday at his home in Princeton, N.J. He was 60. The cause was heart failure, Princeton University said. Mr. Lewis was once dubbed a mad-dog modal realist for his idea that any logically possible world you can think of actually exists. He believed, for instance, that there was a world with talking donkeys.
  13. A Subjectivist's Guide to Objective Chance, Philosophical Papers of David Lewis, Volume 2, Oxford: Oxford University Press, 1986, pp. 83–132.