Nancy Phyllis Cartwright
Nancy Phyllis Cartwright is a prominent contemporary philosopher of science whose work has profoundly shaped how philosophers, scientists, and policy-makers think about laws of nature, causation, and evidence. Trained in both mathematics and philosophy at the University of Pittsburgh, she emerged in the 1970s and 1980s as a leading critic of simple, universalist pictures of scientific laws. In How the Laws of Physics Lie (1983), she argued that many celebrated laws function best as idealized tools within specific models, not as literally true descriptions of the world at all scales. This insight fed into her later ‘dappled world’ thesis, which claims that reality is governed by a patchwork of local regularities, capacities, and causal structures rather than a single unified theory. Moving from physics to economics, social science, and policy, Cartwright has been equally influential in debates about causation and evidence. She developed a robust account of causal powers and criticized naïve reliance on randomized controlled trials, emphasizing that policy success depends on whether causal capacities will “travel” to new contexts. Her work bridges abstract philosophical argument with practical concerns about how to use science responsibly in real-world decision-making, making her a central figure for both philosophers and applied researchers.
At a Glance
- Field
- Thinker
- Born
- 1943-06-24 — Los Angeles, California, United States
- Died
- Active In
- United States, United Kingdom
- Interests
- Laws of natureScientific realismCausationScientific modelsEvidence and inferencePolicy-oriented scienceEconomics and social science methodology
Nancy Cartwright maintains that scientific knowledge is fundamentally local, model-based, and grounded in capacities and causal powers rather than in exceptionless, universal laws; the world is ‘dappled’, structured by a patchwork of limited-scope nomic domains, so understanding and using science—especially for policy—requires pluralistic methods, attention to context, and careful assessment of whether causal capacities will operate in new settings.
How the Laws of Physics Lie
Composed: late 1970s–1983
Nature’s Capacities and Their Measurement
Composed: mid-1980s–1989
The Dappled World: A Study of the Boundaries of Science
Composed: mid-1990s–1999
Hunting Causes and Using Them: Approaches in Philosophy and Economics
Composed: early 2000s–2007
Evidence-Based Policy: A Practical Guide to Doing It Better
Composed: early 2010s–2012
Evidence for Use: Causal Pluralism and Evidence-Based Policy
Composed: 2010s–2021
The laws of physics do not describe regularities in nature; rather, they describe the behavior of highly idealized objects in highly contrived circumstances.— Nancy Cartwright, How the Laws of Physics Lie (Oxford University Press, 1983), Introduction.
Cartwright challenges the traditional assumption that fundamental physical laws straightforwardly capture how things ordinarily behave in the world.
We live in a dappled world, a world rich in different kinds of things, with different natures, behaving in different ways.— Nancy Cartwright, The Dappled World: A Study of the Boundaries of Science (Cambridge University Press, 1999), p. 1.
She introduces her ‘dappled world’ thesis, opposing the idea that a single, unified system of laws governs all phenomena in the same way.
Capacities are what make causes produce their effects; without capacities, laws are idle.— Nancy Cartwright, Nature’s Capacities and Their Measurement (Clarendon Press, 1989), ch. 1.
Cartwright emphasizes that genuine causal powers underwrite the operation of laws, making capacities central to her metaphysics of causation.
Evidence that a policy works somewhere is not yet evidence that it will work for us here.— Nancy Cartwright and Jeremy Hardie, Evidence-Based Policy: A Practical Guide to Doing It Better (Oxford University Press, 2012), ch. 1.
She warns policy-makers against uncritical transfer of results from one context to another, highlighting the problem of external validity.
No one method, no one design, no one kind of evidence is best for answering all causal questions.— Nancy Cartwright, Evidence for Use: Causal Pluralism and Evidence-Based Policy (Oxford University Press, 2021), Conclusion.
Cartwright articulates her pluralist stance on methods and evidence, rejecting rigid evidence hierarchies in favor of context-dependent methodological mixes.
Early Formation in Analytic Philosophy and Physics (1960s–late 1970s)
Cartwright’s early training at the University of Pittsburgh under Adolf Grünbaum immersed her in analytic philosophy of science and the conceptual foundations of physics. During her early Stanford years she engaged deeply with classical and quantum mechanics, acquiring technical expertise that would underpin her later challenges to standard views of scientific laws.
Critique of Laws and Rise to Prominence (late 1970s–late 1980s)
With the publication of *How the Laws of Physics Lie* (1983), Cartwright became a central figure in philosophy of science. She argued that laws are idealized, model-dependent schemata whose apparent universality is misleading, and developed a practice-oriented, pluralistic picture of scientific explanation. *Nature’s Capacities and Their Measurement* (1989) extended this to a realist theory of causal capacities.
From Physics to the ‘Dappled World’ and Social Science (1990s)
After moving to the London School of Economics, Cartwright broadened her focus beyond physics to economics and social science. In *The Dappled World* (1999) she advanced the idea that reality is a patchwork of local nomic domains. This phase consolidated her opposition to global law-based metaphysics and emphasized the limited scope of scientific theories.
Causation, Evidence, and Policy Engagement (2000s–present)
Cartwright increasingly turned to questions about causal inference and evidence in medicine, economics, and social policy. She criticized simplistic hierarchies of evidence centered on randomized controlled trials and advocated a pluralistic, context-sensitive approach. Through leadership roles at LSE, Durham, and research centers like CPNSS and CHESS, she has promoted a philosophy of science that is both metaphysically nuanced and practically engaged with real-world decision-making.
1. Introduction
Nancy Phyllis Cartwright (b. 1943) is a leading contemporary philosopher of science whose work has reshaped debates about laws of nature, causation, scientific models, and evidence. Trained in mathematics and philosophy and active in both the United States and the United Kingdom, she is widely associated with a practice-oriented, pluralist view of science.
Cartwright’s central contention is that scientific knowledge is local and model-based rather than a unified system of exceptionless universal laws. In How the Laws of Physics Lie she argues that many celebrated “laws” in physics are strictly true only in highly idealized circumstances and within specific models. This feeds into her later picture of a “dappled world”—a reality structured by a patchwork of capacities, mechanisms, and limited nomic domains.
Alongside this rethinking of laws, Cartwright has developed a substantive metaphysics and epistemology of causal powers (capacities) and has applied it to the methodology of physics, economics, and social science. Her work on evidence-based policy challenges simple hierarchies that privilege randomized controlled trials, emphasizing instead the importance of mechanisms, context, and the “travel” of causal capacities from study settings to target environments.
Her writings have been central to discussions of scientific realism, causal pluralism, and the role of philosophy in public decision-making. Proponents see her as a major force in redirecting philosophy of science toward actual scientific and policy practice; critics question aspects of her anti-universalism and her treatment of laws and mechanisms. The following sections outline her life, intellectual development, principal works, core ideas, and the debates they have generated.
2. Life and Historical Context
Nancy Cartwright was born on 24 June 1943 in Los Angeles, California, into the postwar generation that would come of age alongside the rapid expansion of physics, computing, and the social sciences. She studied mathematics and philosophy at the University of Pittsburgh, completing her PhD in 1971 under Adolf Grünbaum, a central figure in analytic philosophy of science and the philosophy of physics. This dual training positioned her at the intersection of technical science and philosophical analysis.
Academic Career
Cartwright joined Stanford University in 1973, during a period when philosophy of science was dominated by debates about scientific realism, theoretical reduction, and the status of fundamental physics. Her Stanford years coincided with the consolidation of quantum field theory and the Standard Model in physics, providing a rich empirical backdrop for her early work on the foundations of quantum mechanics and the nature of laws.
In 1991 she moved to the London School of Economics (LSE), an institution historically associated with logical empiricism, decision theory, and economic methodology. This shift brought her into closer contact with economists and social scientists and facilitated her later engagement with policy, development economics, and evidence-based practice. She later held positions at Durham University, helping to found the Centre for Humanities Engaging Science and Society (CHESS).
Historical-Intellectual Setting
Cartwright’s career spans several major transitions in philosophy of science:
| Period | Dominant Themes Relevant to Cartwright |
|---|---|
| 1960s–1970s | Post-positivist debates on realism, explanation, and theory change |
| 1980s–1990s | Renewed interest in scientific practice, models, and pluralism |
| 2000s–present | Focus on causation, mechanisms, evidence hierarchies, and policy relevance |
Her work responds to and participates in all three, contributing to the move from abstract reconstruction of science toward practice-sensitive, interdisciplinary approaches.
3. Intellectual Development
Cartwright’s intellectual trajectory is often described in phases, each marked by a shift in primary scientific interlocutors and philosophical questions, while maintaining continuity in her emphasis on practice, models, and causation.
From Physics Foundations to Laws (1960s–1980s)
Early in her career, Cartwright worked on the foundations of quantum theory and classical mechanics, drawing on her mathematical background. Under the influence of Adolf Grünbaum and contemporaries at Pittsburgh and Stanford, she engaged with questions about probability, measurement, and realism in physics. This period culminated in How the Laws of Physics Lie (1983), where she turned from the interpretation of particular theories to a general critique of laws of nature and idealization.
Capacities and Local Realism (mid-1980s–1990s)
In the mid-1980s Cartwright began articulating a metaphysics of capacities and causal powers, developed systematically in Nature’s Capacities and Their Measurement (1989). Here her focus shifted from laws as regularities to the causal abilities of systems that underwrite and sometimes disrupt regular patterns. This work laid the groundwork for a more explicitly pluralist and local form of scientific realism.
The Dappled World and Beyond Physics (1990s)
After moving to LSE, Cartwright’s attention broadened to include economics and the social sciences. In The Dappled World (1999) she integrated her earlier work on laws and capacities into a broader thesis about the patchy structure of reality. She argued that different scientific domains deploy different models and mechanisms, and that no single nomological system governs them all.
Causation, Evidence, and Policy (2000s–present)
From the 2000s onward, Cartwright increasingly focused on causal inference, methodology, and evidence-based policy. Drawing on her earlier accounts of capacities and mechanisms, she examined how economists, medical researchers, and policy analysts establish that “X works” and whether such claims can be exported to new contexts. Works such as Hunting Causes and Using Them (2007), Evidence-Based Policy (2012, with Jeremy Hardie), and Evidence for Use (2021) reflect this sustained engagement with applied causal reasoning.
4. Major Works
Cartwright’s major monographs trace the evolution of her thinking from laws and models in physics to capacities, causation, and evidence for policy.
How the Laws of Physics Lie (1983)
This book challenges the assumption that fundamental physical laws straightforwardly describe how objects behave in the real world. Cartwright argues that many such laws function as idealized model equations, strictly true only in contrived circumstances. Proponents of her view see this as a pivotal contribution to understanding idealization and modeling; critics question whether it overstates the disconnect between theory and reality.
Nature’s Capacities and Their Measurement (1989)
Here Cartwright develops a theory of capacities (causal powers). She maintains that causes possess stable tendencies to produce certain effects, even when these are masked or not regularly realized. The work links metaphysical claims about capacities to measurement practices in science, especially in economics and social science.
The Dappled World: A Study of the Boundaries of Science (1999)
In this influential book, Cartwright argues that the world is “dappled”: structured by multiple, overlapping local nomological systems rather than a single unified set of laws. She emphasizes bounded scientific domains, the limits of model transfer, and the heterogeneity of mechanisms. The book has been central to discussions of scientific pluralism.
Hunting Causes and Using Them (2007)
This collection examines methods for identifying and employing causes in philosophy and economics. Cartwright contrasts different approaches—manipulationist, probabilistic, and mechanism-based—and explores how they guide inference and policy design.
Evidence-Based Policy (2012) and Evidence for Use (2021)
Co-authored with Jeremy Hardie, Evidence-Based Policy offers a practical guide to using evidence in policy-making, stressing the importance of context, mechanisms, and implementation. Evidence for Use extends these ideas into a systematic account of causal pluralism and evidential pluralism, critiquing simple evidence hierarchies and proposing frameworks for assessing whether causal claims will hold in new settings.
5. Core Ideas: Laws, Models, and the Dappled World
Cartwright’s work on laws and models centers on the claim that what scientists call “laws” often operate primarily within models, not as universal generalizations about all actual systems.
Laws as Model-Based and Idealized
Cartwright contends that canonical laws in physics, such as those of Newtonian mechanics or electrodynamics, describe the behavior of highly idealized systems—frictionless planes, point masses, perfectly isolated charges. In ordinary, messy circumstances, these laws do not strictly hold; instead, they are combined, corrected, and supplemented within models tailored to specific situations.
“The laws of physics do not describe regularities in nature; rather, they describe the behavior of highly idealized objects in highly contrived circumstances.”
— Nancy Cartwright, How the Laws of Physics Lie
Proponents interpret this as a call to distinguish theoretical equations, concrete models, and phenomena. Critics argue that even if laws are idealized, they may still capture real structural features of the world and underpin reliable counterfactuals.
Patchwork or “Dappled” Reality
In The Dappled World, Cartwright extends this analysis into a metaphysical thesis: reality itself is heterogeneous and patchy, governed by different local laws, capacities, and mechanisms in different domains.
| Aspect | Dappled World View |
|---|---|
| Structure of reality | Patchwork of local nomic domains |
| Role of laws | Domain-specific, often tied to models |
| Unity of science | Limited; pluralism across fields |
Supporters see this as making sense of scientific practice, where models and laws are often domain-bound. Alternative views maintain stronger forms of unificationism, holding that underlying universal laws or structures may exist even if they are not fully accessible or explicitly represented in current models.
Cartwright herself tends toward a local or patchwork realism, being realist about specific mechanisms and well-confirmed domain theories while remaining skeptical that a single global theory of everything is either available or needed for scientific success.
6. Capacities, Causation, and Mechanisms
Cartwright’s theory of capacities is central to her account of causation. She holds that causes have real, relatively stable tendencies to produce certain effects, even when these tendencies are not manifested in observable regularities.
Capacities and Causal Powers
In Nature’s Capacities and Their Measurement, capacities are described as the powers or abilities of entities and systems. For example, a drug has the capacity to lower blood pressure; a tax incentive has the capacity to influence investment. These capacities may be masked or offset by other factors, so observed frequencies do not always reveal them straightforwardly.
“Capacities are what make causes produce their effects; without capacities, laws are idle.”
— Nancy Cartwright, Nature’s Capacities and Their Measurement
Advocates see this as revitalizing powers-based metaphysics, contrasting it with Humean regularity theories that identify causation with patterns of constant conjunction, and with purely counterfactual or manipulationist accounts. Critics worry about the ontological and epistemic status of capacities, questioning how they are identified and measured beyond their effects.
Mechanisms and Composing Causes
Cartwright links capacities to mechanisms—organized processes through which capacities operate. In both natural and social sciences, she emphasizes that understanding “what works” requires identifying the mechanism by which it works and the conditions under which the relevant capacities are activated or suppressed.
Her view informs a pluralist stance on causation:
| Approach | Role in Cartwright’s Work |
|---|---|
| Regularity-based | Limited; insufficient where masking and interference are common |
| Counterfactual/manipulationist | Useful for interventions but not exhaustive |
| Mechanism-based | Central for explaining how capacities operate |
| Probabilistic | Important for measurement but interpreted via underlying capacities |
Cartwright’s causal pluralism holds that different causal questions and domains call for different conceptual and methodological tools, with capacities and mechanisms providing a unifying metaphysical backbone.
7. Methodology and Evidence
Cartwright’s methodological work examines how scientists and policy-makers gather and interpret evidence about causal claims, especially in complex social and medical contexts.
Critique of Evidence Hierarchies
Cartwright has been a prominent critic of simple evidence hierarchies that place randomized controlled trials (RCTs) at the top. She acknowledges that RCTs can be powerful tools for establishing that an intervention worked somewhere, but argues that they provide only part of what is needed to know whether it will work elsewhere.
“Evidence that a policy works somewhere is not yet evidence that it will work for us here.”
— Nancy Cartwright & Jeremy Hardie, Evidence-Based Policy
According to Cartwright, hierarchies that rank methods independently of context risk neglecting:
- Differences in populations, institutions, and implementation
- Interaction effects with other policies or background conditions
- Mechanisms through which interventions operate
External Validity and Evidence for Use
Cartwright emphasizes external validity or “travel” of causal claims: whether a finding from one setting will hold in a target setting. In Evidence for Use, she develops frameworks for assembling heterogeneous evidence—quantitative studies, qualitative research, mechanistic understanding, and local knowledge—to judge transferability.
| Question | Cartwright’s Emphasis |
|---|---|
| Did it work there? | RCTs and other causal-identification methods |
| How does it work? | Mechanism and capacity analysis |
| Will it work here? | Context, support factors, and system differences |
This leads to her view of evidential pluralism: no single method suffices for all causal questions.
“No one method, no one design, no one kind of evidence is best for answering all causal questions.”
— Nancy Cartwright, Evidence for Use
Supporters see this as a nuanced guide for policy-oriented research; some methodologists worry that it may weaken clear standards of evidence or complicate decision-making procedures.
8. Impact on Economics, Social Science, and Policy
Cartwright has exerted significant influence on economics, social science methodology, and evidence-based policy, particularly through her work at LSE and Durham.
Economics and Social Science Methodology
In economics, Cartwright has engaged with issues such as:
- The role of structural models and ceteris paribus clauses
- The interpretation of econometric evidence in terms of capacities and mechanisms
- The extent to which economic laws or regularities are domain-bound
Her book Hunting Causes and Using Them examines how economists identify causes (e.g., through natural experiments or instrumental variables) and how these causes are subsequently deployed in policymaking. Economists interested in philosophy of econometrics and model-based reasoning have drawn on her analyses to argue for more explicit consideration of mechanisms and background conditions.
Evidence-Based Policy and Development
Cartwright’s work has been particularly influential in debates about evidence-based policy (EBP) in public health, education, and international development. Through collaborations with policy researchers and organizations, and via the practical guide Evidence-Based Policy, she has promoted:
- Contextual analysis of whether interventions are implementable and supported in target settings
- Systematic assessment of support factors (e.g., institutional capacity, infrastructure)
- Use of mixed-methods evidence to supplement trial results
Her critique of uncritical reliance on RCTs has resonated with scholars and practitioners concerned about the transferability of development interventions and social programs.
Institutional and Interdisciplinary Roles
Cartwright has co-founded or led centers such as the Centre for the Philosophy of Natural and Social Science (CPNSS) at LSE and CHESS at Durham, fostering collaborations among philosophers, economists, statisticians, and policy analysts. These initiatives have encouraged the integration of philosophy of science into applied research design, influencing how agencies and research consortia conceptualize evidence and causality in practice.
9. Criticisms and Debates
Cartwright’s work has generated extensive commentary and debate across philosophy of science, metaphysics, and methodology.
Laws, Models, and the Dappled World
Critics of How the Laws of Physics Lie and The Dappled World raise several concerns:
- Underestimation of unity: Some argue that Cartwright underestimates the extent to which seemingly local models reflect deeper, more unified laws or structures, pointing to successful unification in physics as evidence.
- Ambiguity about “lying”: Others contend that describing laws as “lying” is misleading, since idealizations can still be approximately true or true of underlying structures.
- Patchwork vs. unified realism: Defenders of Humean or structural realism suggest that an underlying unified ontology may coexist with local modeling practices.
Proponents of Cartwright’s view respond that her claims are primarily about how science functions in practice and that any deeper unity remains speculative relative to the richly documented heterogeneity of models and mechanisms.
Capacities and Powers
Cartwright’s capacities-based metaphysics has been both influential and contested. Supporters link it to broader dispositionalist and powers-based trends in metaphysics. Critics question:
- Whether positing capacities goes beyond what is warranted by data
- How to individuate and measure capacities in complex systems
- Whether capacities risk reintroducing a form of occult properties
Alternative accounts—such as counterfactual, interventionist, or probabilistic theories of causation—often propose that their frameworks can capture the same phenomena without invoking robust ontological powers.
Methodology and Evidence-Based Policy
Cartwright’s critique of RCT-centered evidence hierarchies has sparked debate in medicine and policy science. Some methodologists welcome her evidential pluralism; others worry that:
- Emphasizing context and mechanisms might complicate decision rules
- De-emphasizing RCTs could weaken standards against bias
- Her proposals for integrating diverse evidence lack fully operational decision procedures
These debates concern how best to balance rigor, practicality, and contextual sensitivity in real-world decision-making.
10. Legacy and Historical Significance
Cartwright is widely regarded as a central figure in late 20th- and early 21st-century philosophy of science, with a legacy spanning conceptual, methodological, and institutional dimensions.
Reorientation of Debates on Laws and Models
Her insistence that many scientific laws are model-bound and idealized has contributed to a broader shift from focusing on axiomatic theories to examining scientific modeling practices. This has influenced work on:
- The epistemology of idealization and approximation
- The distinction between theories, models, and phenomena
- Practice-oriented, historically informed philosophy of science
Contributions to Realism and Pluralism
Cartwright’s patchwork or local realism has provided a prominent alternative to both strong unificationist realism and global anti-realism. Her dappled world thesis is a touchstone in discussions of:
- Scientific pluralism, where different sciences employ distinct conceptual frameworks
- The feasibility and desirability of a unified science
Even those who disagree with her conclusions often engage with her arguments as a key reference point when articulating their own positions on realism and unity.
Causation, Evidence, and Policy
By linking metaphysical ideas about capacities and mechanisms to concrete issues in econometrics, medicine, and policy, Cartwright has helped establish a model of philosophy of science that is both theoretically sophisticated and practically engaged. Her influence can be seen in:
- Methodological discussions of causal inference and external validity
- Institutional settings where philosophers collaborate with practitioners
- Training materials and frameworks used in evidence-based policy analysis
Historical assessments typically situate Cartwright among the leading architects of a practice-centered, pluralist philosophy of science, whose impact extends beyond academic philosophy into the ways scientists and policy-makers think about laws, causation, and evidence.
How to Cite This Entry
Use these citation formats to reference this thinkers entry in your academic work. Click the copy button to copy the citation to your clipboard.
Philopedia. (2025). Nancy Phyllis Cartwright. Philopedia. https://philopedia.com/thinkers/nancy-cartwright/
"Nancy Phyllis Cartwright." Philopedia, 2025, https://philopedia.com/thinkers/nancy-cartwright/.
Philopedia. "Nancy Phyllis Cartwright." Philopedia. Accessed December 11, 2025. https://philopedia.com/thinkers/nancy-cartwright/.
@online{philopedia_nancy_cartwright,
title = {Nancy Phyllis Cartwright},
author = {Philopedia},
year = {2025},
url = {https://philopedia.com/thinkers/nancy-cartwright/},
urldate = {December 11, 2025}
}Note: This entry was last updated on 2025-12-10. For the most current version, always check the online entry.