David Kellogg Lewis

1. Introduction

David Kellogg Lewis (1941–2001) is widely regarded as one of the central figures of late twentieth‑century analytic philosophy. Working primarily in metaphysics and philosophy of language, he developed an unusually systematic body of theory that uses possible worlds, counterfactuals, and Humean supervenience to analyze a broad range of philosophical phenomena.

Lewis is best known for modal realism, the view that all possible worlds are concrete, spatiotemporal entities on a par with the actual world. He defended this seemingly extravagant ontology on the grounds that it enables simple, uniform treatments of modality, laws of nature, causation, personal identity, and semantic content. His work on counterfactuals provided a now-standard possible‑worlds semantics for “what would have happened if…” statements, with far‑reaching consequences for metaphysics and philosophy of science.

Alongside these metaphysical projects, Lewis contributed influential accounts of convention, language, and social coordination, drawing on decision theory and game theory. He also published significant papers on mind, probability, value theory, and mereology, often integrating these topics into his overarching metaphysical picture.

Lewis’s writings are frequently cited not only for their specific doctrines but also for their methodological clarity and rigor. Philosophers who reject modal realism or his Humean views on laws typically frame their alternative positions in explicit contrast to Lewis’s system, and they often appropriate his technical tools. His work therefore functions as a reference point across many debates in contemporary analytic philosophy.

2. Life and Historical Context

Lewis was born in 1941 in Oberlin, Ohio, into an academically and politically engaged family. He studied at Swarthmore College, then spent a formative year (1961–62) at Oxford, where participation in seminars by figures such as J. L. Austin and Iris Murdoch acquainted him with ordinary‑language philosophy and rigorous argumentative practice. Returning to the United States, he completed his PhD at Harvard under W. V. O. Quine in 1967, before joining UCLA and then, in 1970, Princeton University, where he remained until his death in 2001.

2.1 Academic and Intellectual Milieu

Lewis’s career unfolded during a period when analytic philosophy was consolidating its dominance in the Anglophone world, and when skepticism about intensional notions (modality, meaning, propositional attitudes) was still prominent, partly under Quine’s influence. At the same time, modal logic, possible‑worlds semantics, and formal decision theory were rapidly developing.

His work emerged at the intersection of these trends:

2.2 Institutional Setting

Princeton in the 1970s–1990s became a major hub of analytic metaphysics and philosophy of language, with Lewis as a central figure. His regular visits to Australian departments—especially in Sydney and Canberra—fostered strong trans‑Pacific connections and helped make Australia an important center for Lewis‑influenced metaphysics.

Lewis’s later years were marked by serious health problems, including complications from diabetes, but he remained philosophically active, publishing and corresponding until shortly before his death in 2001.

3. Intellectual Development

Lewis’s intellectual trajectory is often described in terms of overlapping phases, each marked by characteristic projects but unified by a stable commitment to systematic theorizing and formal tools.

3.1 Early Formation (1940s–mid‑1960s)

As a student at Swarthmore and Oxford, Lewis encountered both formal logic and ordinary‑language philosophy. At Harvard, under Quine, he absorbed a naturalistic outlook and an emphasis on regimenting discourse into formal languages. However, he gradually diverged from Quine’s suspicion of modality, becoming increasingly convinced that modal and intensional notions could be treated with full theoretical seriousness.

3.2 Convention and the Turn to Possible Worlds (late 1960s–mid‑1970s)

Lewis’s dissertation, later published as Convention (1969), used decision and game theory to analyze social and linguistic regularities as coordination equilibria. During this period he also began systematically employing possible‑worlds models in semantics, most prominently in Counterfactuals (1973). His work on counterfactuals, causation, and tensed language in these years started to reveal an emerging unified metaphysical framework.

3.3 Systematic Modal Metaphysics (mid‑1970s–late 1980s)

From the mid‑1970s, Lewis developed his distinctive modal realism, culminating in On the Plurality of Worlds (1986). Articles on counterpart theory, personal identity, properties and naturalness, and laws of nature were woven into a single metaphysical picture. His essays from this period also articulated Humean supervenience and the best system account of laws, integrating metaphysics with philosophy of science.

3.4 Later Extensions and Refinements (late 1980s–2001)

In his later work, Lewis expanded his system to mereology and foundations of mathematics (Parts of Classes, 1990), refined his views on mental content, probability, and decision theory, and responded to objections to modal realism and Humeanism. Collections such as Philosophical Papers and Papers in Metaphysics and Epistemology exhibit both continuity with and critical refinement of his earlier positions.

4. Major Works

This section outlines Lewis’s principal book‑length works and main collections, indicating their thematic roles within his corpus.

4.1 Monographs

4.2 Collections of Papers

Lewis’s influential articles were gathered into several volumes, which function as thematic companions to his monographs.

These works collectively exhibit Lewis’s strategy of developing interconnected accounts: treatments of convention and counterfactuals support his views on causation and laws; those in turn presuppose his broader modal and mereological ontology. Later papers often refine or qualify doctrines initially presented in the monographs, while still operating within a largely unified framework.

5. Core Ideas and Metaphysical System

Lewis’s metaphysical system is organized around several interconnected theses, most notably modal realism, counterpart theory, and Humean supervenience.

5.1 Modal Realism and Possible Worlds

Lewis treats possible worlds as concrete, spatiotemporal wholes, each as real as the actual world. According to him, modal statements (about what is possible or necessary) are made true by facts about these worlds:

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We are to think of other possible worlds as of other times or other places.

— Lewis, On the Plurality of Worlds

On this view, there is a vast plurality of worlds, each containing its own individuals and laws, and “actual” simply picks out the world we inhabit.

Proponents emphasize the uniformity and reductive power of this picture: it provides a single ontology to underwrite modal talk, counterfactuals, properties, and propositions. Critics argue that it is ontologically extravagant or conflicts with common sense; Lewis replies by appealing to theoretical virtues such as simplicity of theory and explanatory reach.

5.2 Counterpart Theory

To handle cross‑world identity, Lewis rejects strict trans‑world identity in favor of counterpart theory. An individual “being a certain way in another world” is analyzed as there being a similar individual—the counterpart—in that world. This supports flexible treatments of de re modality and personal identity, while preserving the idea that each world is self‑contained.

5.3 Humean Supervenience and the Mosaic

Another core idea is Humean supervenience: all facts, including those about laws, causation, and modality, supervene on a “mosaic” of local, particular qualities arranged in space‑time. Higher‑level phenomena are patterns in, or best descriptions of, this mosaic rather than additional ontological ingredients.

This picture underlies his best system account of laws, his reductionist views of chance and causation, and his preference for sparse, “natural” properties. The result is a systematic metaphysical framework in which many philosophical topics are analyzed in terms of worlds, individuals, and their arrangement within a Humean mosaic.

6. Language, Convention, and Social Theory

Lewis’s contributions to language and social theory center on conventions and their role in meaning, communication, and coordination.

6.1 Lewisian Conventions

In Convention (1969), Lewis characterizes a convention as a regularity in behavior that solves a coordination problem because everyone expects others to conform and prefers to conform given those expectations. Formally, this is modeled using coordination games from game theory.

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A convention is a regularity in action that solves a coordination problem because everyone expects everyone else to conform and prefers to conform on condition that others do.

— Lewis, Convention

This account explains how social and linguistic norms can arise without explicit agreement, legislation, or innate programming. Examples include driving on a particular side of the road or using words with particular meanings.

6.2 Language as a System of Conventions

Lewis applies this framework to language by treating a language as a system of conventions about word use. A sentence means what it does because speakers in a community have converged on coordinated patterns of use, sustained by mutual expectations and preferences for successful communication.

He develops tools such as signaling games and common knowledge to analyze how speakers coordinate on interpretations, and how new conventions can emerge or shift. This approach influenced subsequent work on the philosophy of language, social ontology, and the interface between economics and linguistics.

6.3 Extensions to Social Theory

Lewis’s analysis has been extended by others to norms governing social practices more generally. Proponents see it as illuminating the structure of informal rules and institutions; critics question whether all norms are best understood as coordination equilibria or whether the decision‑theoretic assumptions fit complex social phenomena. Nonetheless, his framework remains a standard reference in debates about the nature and origin of social rules.

7. Causation, Laws, and Humean Supervenience

Lewis’s treatments of causation and laws of nature are tightly connected to his broader commitment to Humean supervenience.

7.1 Counterfactual Analysis of Causation

In his 1973 paper “Causation” and later refinements, Lewis analyzes causal relations in terms of counterfactual dependence between events. Roughly, event C causes event E if, had C not occurred, E would not have occurred (or would have been different), evaluated via his similarity‑based semantics for counterfactuals.

He later allows for chains of dependence and influence to address preemption and other problem cases. Supporters value the unification of causation with counterfactual semantics; critics point to difficulties with probabilistic causation, overdetermination, and the dependence of causal facts on a context‑sensitive similarity relation.

7.2 Best System Account of Laws

Lewis’s best system account characterizes laws of nature as the theorems of the simplest, strongest systematization of all particular facts (“the Humean mosaic”). A law is a regularity that appears as an axiom or theorem in the system that optimally balances simplicity and explanatory strength.

This approach aims to reconcile Humeanism—no necessary connections in nature—with the apparent objectivity of laws. Critics argue that the account is too descriptive, struggles with probabilistic laws, or makes lawhood overly relative to standards of simplicity.

7.3 Humean Supervenience and Chance

Lewis extends the best system idea to chance, treating objective probabilities as features posited by the best system that balances simplicity with accurate probabilistic predictions. All facts about laws, chance, and causal relations thus supervene on the underlying distribution of local qualities in space‑time. Alternatives to this view include non‑Humean theories that take laws or powers as fundamental entities not reducible to the Humean mosaic.

8. Methodology and Theoretical Virtues

Lewis’s philosophical practice is notable for its explicit appeal to theoretical virtues and its quasi‑scientific style of model building.

8.1 Cost–Benefit Ontology

Lewis famously frames metaphysical theorizing as a kind of cost–benefit analysis. Ontological commitments are “costs”; explanatory power, simplicity, and systematicity are “benefits.” He maintains that even seemingly extravagant ontologies, such as modal realism, may be warranted if they yield substantial theoretical payoffs.

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We are not forced to choose between an unacceptably strong ontology and an unacceptably weak theory; we must weigh the costs of ontology against the benefits of theory.

— Lewis, On the Plurality of Worlds

8.2 Theoretical Virtues

Key virtues Lewis invokes include:

8.3 Reliance on Intuitions and Thought Experiments

Like many analytic philosophers, Lewis takes intuitions about cases (e.g., in modal and causal scenarios) as important data, but he also emphasizes that they can be overridden by superior theoretical organization. His frequent use of model‑building—constructing possible‑worlds frameworks, game‑theoretic setups, and mereological systems—has been taken as a model for rigorous, explicit theorizing.

Supporters see his methodology as exemplifying a disciplined, transparent balancing of commitments. Critics contend that the weighting of virtues is underdescribed, that common‑sense intuitions receive too much (or too little) authority, or that formal models may obscure as much as they reveal.

9. Impact on Analytic Metaphysics and Related Fields

Lewis’s influence extends across metaphysics, philosophy of language, mind, and adjacent disciplines.

9.1 Metaphysics and Modality

In metaphysics, Lewis’s possible‑worlds framework became a default idiom for discussing modality, counterfactuals, and de re properties, even among philosophers who reject modal realism. Debates about actualism vs. modal realism, trans‑world identity vs. counterpart theory, and Humean vs. non‑Humean laws are frequently framed against his positions.

His work helped revive and reshape analytic metaphysics in the 1970s–1990s, encouraging detailed exploration of persistence, composition, properties, and grounding. Many contemporary metaphysical systems adapt Lewisian tools while altering key commitments (e.g., adopting ersatz possible worlds, or non‑Humean laws).

9.2 Philosophy of Language and Mind

In philosophy of language, his accounts of convention, truth conditions, and context‑sensitivity influenced theories of meaning, reference, and communication. Possible‑worlds semantics for intensional operators (belief, desire, obligation) became standard, often drawing on his formal frameworks.

In philosophy of mind, Lewis’s work on psychophysical identity, functionalism, and content contributed to physicalist and representationalist approaches. His treatment of mental content via causal and counterfactual relations influenced later debates on externalism and naturalization of meaning.

9.3 Decision Theory, Game Theory, and Social Ontology

Lewis’s use of decision theory and game theory in Convention left a lasting mark on both philosophy and, indirectly, on economics and political theory. His models of coordination and signaling informed later work on common knowledge, signaling games, and social norms.

Beyond specific doctrines, Lewis’s systematic style has shaped how many philosophers approach theory choice, the use of formal models, and the evaluation of ontological costs. His work is widely taught, and engagement with his views is a standard part of training in analytic metaphysics and related fields.

10. Criticisms and Alternatives to Lewis’s Framework

Lewis’s system has prompted extensive criticism and the development of alternative theories across multiple domains.

10.1 Objections to Modal Realism

Critics often target the ontological extravagance of positing a vast plurality of concrete worlds. Many argue that common sense and parsimony favor actualism, which denies the existence of non‑actual concrete worlds. Alternatives include:

Some critics also challenge counterpart theory, arguing that it conflicts with ordinary intuitions about identity across worlds or undermines certain de re modal claims.

10.2 Challenges to Humean Supervenience and Laws

Lewis’s Humean supervenience faces opposition from non‑Humean accounts of laws and modality, which posit irreducible laws, powers, or dispositions. Proponents of these views contend that the best system account cannot adequately capture the necessitating or governing aspect of laws, or the explanatory role of causal powers.

Alternatives include Armstrong‑style nomic necessitation, dispositional essentialism, and views that treat laws as metaphysically primitive. Critics argue that Humeanism struggles with probabilistic laws, counterfactual support, and the apparent asymmetry between laws and accidental regularities.

10.3 Critiques of Methodology and Use of Intuitions

Some philosophers question Lewis’s cost–benefit approach to ontology, arguing that there is no neutral way to weigh simplicity, strength, and ontological commitment. Others worry that his reliance on possible worlds and model‑theoretic methods may obscure the connection between metaphysics and empirical inquiry.

There are also debates about the evidential role of intuitions in his case‑based reasoning, with some critics pushing for more empirically informed or practice‑based approaches. Nonetheless, even those who reject key elements of Lewis’s framework often adopt his style of explicit, virtue‑guided theory comparison when articulating alternatives.

11. Legacy and Historical Significance

Lewis’s legacy is marked by both the direct adoption of his ideas and the way his work structured subsequent debates.

11.1 Doctrinal Legacy

Many elements of contemporary analytic philosophy trace directly to Lewis:

• Possible‑worlds discourse has become standard in discussions of modality, counterfactuals, and intensionality, often using Lewisian formal tools even when rejecting modal realism.
• The counterfactual analysis of causation and the best system account of laws remain central reference points in philosophy of science and metaphysics.
• His analysis of convention continues to inform work on language, social norms, and coordination.

11.2 Methodological Influence

Lewis’s explicit appeal to theoretical virtues and his systematic use of model‑building have contributed to a conception of philosophy as pursuing theories that resemble scientific models in clarity and structure. Many researchers, including his students and interlocutors, have adopted this style, whether or not they accept his substantive conclusions.

11.3 Place in the History of Analytic Philosophy

Historically, Lewis is often grouped with figures like Kripke and Putnam as part of a generation that re‑legitimized metaphysics within analytic philosophy. His work helped move the subject from a relatively austere, Quinean landscape to a richer terrain in which questions about possibility, laws, and properties could be tackled with formal sophistication.

His influence is especially strong in Anglophone departments in the United States and Australia, where “Lewisian” frameworks are common reference points in teaching and research. Posthumous collections and ongoing critical engagement ensure that his system continues to serve both as a model to be developed and as a foil against which alternative metaphysical and methodological outlooks are articulated.