A Treatise Concerning the Principles of Human Knowledge, Part I

1. Introduction

A Treatise Concerning the Principles of Human Knowledge, Part I is George Berkeley’s most systematic presentation of his immaterialist metaphysics and epistemology. In this work he proposes that all the immediate objects of human awareness are ideas and that what philosophers have called material substance is an unnecessary and unintelligible posit.

Berkeley opens the Treatise by diagnosing what he takes to be the central ills of early modern philosophy: skepticism about the external world, abstruse metaphysical disputes, and the perceived tendency of philosophy to undermine religion and morality. He attributes these problems, in large part, to the concept of matter understood as a mind‑independent substratum.

The Introduction frames several core aims:

• To show that seemingly paradoxical philosophical doctrines about matter and abstraction arise from linguistic and conceptual confusion.
• To defend an empiricist principle that all meaningful content must be traceable to experience.
• To demonstrate that abandoning material substance does not threaten common life, science, or religion, but instead places them on firmer ground.

Berkeley presents his project as both negative and positive: negatively, he seeks to expose certain key notions—such as abstract ideas and unthinking matter—as devoid of clear content; positively, he outlines an ontology consisting only of spirits (minds) and their ideas, governed by a divinely ordered regularity.

The introduction also signals Berkeley’s methodological stance. He repeatedly calls for “clearness and precision” in the use of terms and encourages readers to reflect on their own experiences rather than rely on inherited metaphysical vocabulary. Commentators often regard this self‑conscious emphasis on linguistic clarification as an important bridge between early modern metaphysics and later philosophy of language.

2. Historical Context and Intellectual Background

Berkeley’s Treatise emerges from, and reacts to, several overlapping intellectual currents in the late seventeenth and early eighteenth centuries.

Empiricism and Locke

John Locke’s Essay Concerning Human Understanding (1690) forms the most immediate background. Locke’s theory of ideas, his distinction between primary and secondary qualities, and his account of abstract general ideas provide both Berkeley’s framework and his targets. Berkeley accepts an empiricist starting point—ideas as the contents of experience—but rejects Locke’s allowance for unknowable material substrata and abstract ideas.

Rationalism and Metaphysics

On the Continent, rationalists such as Descartes, Malebranche, and Leibniz developed metaphysical systems involving substance dualism, occasionalism, or monads. Berkeley engages selectively with these views—especially Malebranche’s occasionalism and doctrine of seeing all things in God—while resisting their appeal to innate ideas and speculative metaphysics. Some interpreters see Berkeley as mediating between empiricism and rationalism by combining sensory foundations with a robust theistic metaphysics.

Scientific Revolution

The Treatise was written in the wake of Newtonian mechanics. Natural philosophers increasingly described the world in mathematical, mechanistic terms, often coupled with a cautious or skeptical stance toward traditional metaphysics. Berkeley accepts the success of mathematical physics but contends that its explanatory power does not require commitment to material substance, mechanical corpuscles, or absolute space. His reinterpretation of laws of nature as regularities among ideas responds to this context.

Religious and Theological Debates

Berkeley wrote within Anglican Ireland, during controversies over deism, free‑thought, and skepticism about revelation. He presents immaterialism as supportive of providence and divine activity against views that treat the physical world as a self‑sufficient system. Historians disagree over how primarily theological his motivations were: some stress apologetic goals, others highlight internal philosophical pressures within empiricism.

3. Author, Composition, and Publication

Berkeley’s Intellectual Development

George Berkeley (1685–1753), an Irish philosopher and Anglican clergyman, was educated and then appointed Fellow at Trinity College Dublin. Before the Treatise, he published An Essay Towards a New Theory of Vision (1709), where he developed an empiricist account of visual perception and distance. Many scholars view that essay as a preparatory study, anticipating the immaterialist claims of the Treatise while remaining more cautious in its metaphysical commitments.

Composition and Aims

The Treatise was composed roughly between 1706 and 1710. Surviving notebooks and correspondence suggest that Berkeley gradually moved from reflections on perception and mathematics to a comprehensive rejection of material substance. He conceived the work as the first part of a larger project; a second, never‑published part was intended to address ethics and the passions.

Berkeley’s stated aims in the Preface and Introduction include clarifying the “principles of human knowledge,” dissolving skepticism, and defending religion. Some commentators emphasize a didactic, almost pastoral aim; others stress his ambition to reshape metaphysics and epistemology at a foundational level.

Publication Details

The book appeared in octavo format, a common size for learned works. The anonymity has been interpreted in various ways: as a protective measure given the work’s radical theses, as a conventional modesty, or as a way to allow the arguments to stand on their own.

Later Treatments and Related Texts

Berkeley later re‑presented and defended similar doctrines in the Three Dialogues between Hylas and Philonous (1713), a more accessible, dialogical work, and in Latin writings such as De principiis humanæ cognitionis. Scholars often read these texts alongside the Treatise to track changes of formulation, especially regarding notions of spirit and the role of language. There is ongoing debate about whether Berkeley significantly revised his views or mainly clarified them for different audiences.

4. Structure and Organization of the Treatise

Part I of the Treatise is organized into a Preface, an Introduction, and 156 numbered sections, of which only the first 84 are devoted to “the principles of human knowledge” in the narrower sense that concerns epistemology and metaphysics. The remainder addresses further topics such as mathematics and natural philosophy, which are sometimes treated separately by commentators.

Overall Architectural Plan

Within Part I, interpreters commonly distinguish several thematic blocks:

The overlaps—such as §§10–17 being both part of the argument against matter and the attack on abstract ideas—reflect Berkeley’s non‑linear exposition. He often interweaves discussions of perception, language, and metaphysics rather than treating them in isolation.

Method of Presentation

Berkeley adopts a numbered‑section format rather than extended chapters. This arrangement allows him to:

• Introduce short, self‑contained theses.
• Return to themes from different angles.
• Anticipate and respond to objections in an incremental fashion.

Some scholars view this as echoing the aphoristic style of Descartes’ Principles of Philosophy, while others see it as suited to Berkeley’s pedagogical and apologetic purposes.

Relation to the Unwritten Second Part

Berkeley announced that a second part would address ethics and the passions, building upon the principles established in Part I. Although never published, this promise indicates his intention to derive a broader moral and practical philosophy from his immaterialist foundations. This projected continuation has influenced interpretations of the unity of the work, with some commentators reading even the early metaphysical sections as oriented toward later ethical and religious applications.

5. Objects of Human Knowledge and the Nature of Ideas

In the opening sections (§§1–7), Berkeley sets out what he calls the objects of human knowledge and clarifies the basic elements of his ontology.

Ideas as Immediate Objects of Knowledge

Berkeley begins by stating that all objects of human knowledge fall under three heads: sense, reflection, and imagination. The things immediately perceived in these ways he calls ideas. They include sensory qualities (colors, sounds, tastes), passions and operations of the mind as reflected upon, and images formed in memory or imagination.

He emphasizes that ideas are:

• Passive: they are suffered or received; they do not act.
• Particular: each idea is a determinate instance, not a vague or indeterminate entity.
• Mind‑dependent: they exist only insofar as they are perceived.

Distinction Between Ideas and Spirits

Against this background, Berkeley introduces a distinction between ideas and spirits (§2). While ideas are passive and perceived, spirits (or minds) are:

• Active: capable of willing, understanding, and causing ideas to appear.
• Simple and indivisible: not composed of parts as ideas are.
• Not themselves ideas: they are known not by being pictured or imagined but by a different kind of awareness.

Berkeley writes:

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“I find I can excite ideas in my mind at pleasure and vary and shift the scene as oft as I think fit. It is no more than willing, and straightway this or that idea arises in my fancy; and by the same power it is obliterated, and makes way for another.”

— Berkeley, Principles, §28 (illustrative of his idea/spirit contrast, though from later in the text)

This contrast underlies the later claim that the world consists of two kinds of entity only: ideas and spirits.

Early Steps Toward Immaterialism

Already in these initial sections, Berkeley hints that sensible things—tables, trees, and the like—are nothing but collections or combinations of ideas perceived by some spirit. He does not yet deny matter explicitly, but by restricting the objects of knowledge to ideas, he prepares the ground for questioning what content, if any, the notion of an unperceived material substratum could have. Commentators sometimes describe this as an “ideational starting point” from which the more radical immaterialist theses will follow.

6. The Critique of Material Substance and Esse Est Percipi

From roughly §§8–24, Berkeley develops his attack on material substance and formulates the thesis commonly summarized as esse est percipi (“to be is to be perceived”).

Inconceivability of Material Substance

Berkeley argues that, given his earlier restriction of knowable objects to ideas, the notion of a material substratum underlying sensible qualities lacks any clear content. When philosophers speak of a material substance in which colors, shapes, and motions inhere, they appear to posit:

• A support that is itself never perceived.
• Something distinct from the very ideas that constitute sensible experience.

Berkeley contends that one cannot form an idea of such a substratum without smuggling in the sensible qualities themselves. Since all ideas are particular sensory or reflective contents, any alleged idea of “bare” material substance either reduces to a collection of sensible qualities (which are acknowledged ideas) or is a mere word.

Esse Est Percipi

Against this background, Berkeley advances his central formula:

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“Their esse is percipi, nor is it possible that they should have any existence, out of the minds or thinking things which perceive them.”

— Berkeley, Principles, §3

This thesis concerns sensible things: colors, sounds, tangible objects. Their existence consists in being perceived by some mind. When such things are not perceived by finite spirits like humans, Berkeley will later say their continued existence is grounded in God’s perception. Within §§8–24, however, the primary emphasis falls on the dependence of sensible objects on perception as such.

Rejection of Unperceived Objects

Berkeley challenges the common belief that houses, mountains, and rivers might exist altogether unperceived. He invites readers to attempt to conceive of such objects existing unperceived and argues that, in doing so, one still imagines them as perceived by oneself or another observer. Critics maintain that this confuses what is conceived with the conditions of its existence; defenders hold that it exposes the incoherence of mind‑independent matter within an empiricist framework.

Role in Anti‑Skeptical Strategy

Berkeley associates material substance with skepticism. If sensible qualities are supposed to be mere appearances caused by an unknowable material world behind them, then knowledge of reality becomes precarious. By identifying reality with the ideas immediately perceived and the spirits that perceive them, he aims to remove this gap. Commentators disagree about how successful this maneuver is in answering skeptical worries, but they generally agree that it is central to his overall project.

7. Abstract Ideas, Generality, and Language

In §§10–17 (with some overlap elsewhere), Berkeley presents a sustained critique of abstract general ideas, targeting particularly John Locke’s doctrine. This section of the Treatise also advances a positive account of generality and the function of language.

Critique of Abstract General Ideas

Locke had argued that the mind forms abstract ideas—such as that of “triangle in general”—by leaving out specific features (right‑angled, equilateral, etc.) and retaining only what is common. Berkeley contends that this psychological description is mistaken:

• Any imagined triangle must be determinate in some respect (e.g., scalene or isosceles).
• We cannot literally picture an object that is simultaneously all and none of these determinate kinds.

He concludes that the supposed ability to form abstract ideas is a fiction produced by verbal confusion rather than an accurate report of mental operations.

Generality as Use of Signs

Berkeley replaces abstract ideas with a theory of general signs. A word or idea is general not by being indeterminate in itself but by being used to stand indifferently for many particular ideas. For example, the word “triangle” is applied to all particular triangles by a convention of language.

Implications for Metaphysics

Berkeley applies this critique to terms like “substance,” “extension,” “matter,” and “space in general.” He argues that philosophers have supposed themselves to possess abstract ideas corresponding to these words, when in fact no such ideas can be produced. According to him, once one recognizes that all ideas are particular, many traditional metaphysical debates lose their foundation.

Later commentators differ on the reach of this argument. Some think it undermines the very possibility of certain kinds of metaphysics; others interpret Berkeley as allowing meaningful general discourse, including scientific law statements, provided it is understood in terms of the use of signs rather than imaginary abstract entities.

8. Perception, Sensible Qualities, and Relativity

Berkeley’s discussion of perception and the relativity of sensible qualities (notably in §§9, 14–20) supports his case against materialism by arguing that all such qualities depend on perceivers and conditions.

Variability of Sensible Qualities

Berkeley highlights familiar phenomena: the same water feels hot to one hand and cold to the other, a color looks different in bright sunlight and in shadow, an object appears smaller at a distance than up close. From such examples he infers that:

• Sensible qualities vary systematically with the organs and perspective of the perceiver.
• If qualities were inherent in a mind‑independent material substance, they would not exhibit this kind of relativity.

He argues that attempts to rescue material qualities by assigning some as “real” (primary) and others as merely “appearance” (secondary) are unstable. The same relativity that affects color and taste, he maintains, also affects extension, shape, and motion.

Challenge to the Primary/Secondary Quality Distinction

Locke’s primary/secondary distinction treats extension, figure, and motion as objective features of bodies, while colors, sounds, and tastes derive from the interaction between bodies and perceivers. Berkeley counters that our ideas of extension and motion are no less dependent on perceptual conditions (e.g., the resolution of vision, bodily scale, and relative frames of reference) than colors or sounds.

Proponents of Berkeley read this as dissolving one of the main supports for materialism: once all sensible qualities are equally mind‑dependent, it becomes harder to ascribe them to an underlying physical reality distinct from ideas. Critics respond that variations in perceptual appearance do not preclude stable, underlying properties describable by physics.

Perception and Order

While emphasizing relativity, Berkeley also stresses the regularity and predictability in how ideas change with conditions, an aspect that will underwrite his later interpretation of laws of nature. The interplay of variation and order in perception thus serves a dual purpose: undermining the materialist picture of inhering qualities, while preparing the way for a non‑materialist account of the physical world as a system of ideas governed by stable rules.

9. Spirits, God, and the Order of Nature

After establishing that sensible things are collections of ideas, Berkeley turns in §§25–33 to spirits and the divine ordering of nature.

Spirits as Active Substances

Berkeley holds that, unlike ideas, spirits are active, non‑sensible entities that perceive, will, and understand. Human minds are known, he claims, not through ideas of them but via an immediate notion we have of ourselves as agents. This notion includes awareness of our ability to excite certain ideas (e.g., images in imagination) and to act on our bodies.

Spirits differ from ideas in several respects:

• They are simple and indivisible, not extended or composed of parts.
• They are causes of ideas (at least some ideas, such as imaginative ones).
• They are not objects of sense; they are known reflectively.

Argument for the Existence of God

Berkeley argues that many of our ideas—especially those of the sensory world—are not under our control. Since ideas themselves are passive, there must be some active being that causes the orderly sequence of sensory ideas when we open our eyes, touch objects, or hear sounds.

He infers the existence of an infinite spirit—God—who:

• Produces and coordinates the sensory ideas we experience.
• Is omnipresent in the sense of perceiving all things.
• Guarantees the continued existence of sensible objects when no finite mind perceives them.

This line of reasoning has been read both as a design‑style argument from the orderliness of nature and as an inference from the causal structure of experience. Some commentators regard it as central to Berkeley’s system; others treat it as less rigorously developed than his negative attack on matter.

The Order of Nature

For Berkeley, the order of nature consists in the regular ways in which God causes ideas to appear to finite spirits. The stability and law‑likeness of these sequences allow prediction, practical action, and scientific theorizing. Nature becomes, in effect, a common framework of divine communication shared among spirits.

Later interpreters disagree about how literally to take Berkeley’s talk of divine volitions and whether his view aligns more closely with traditional occasionalism or with a distinct form of theism grounded in his notion of ideas and spirits.

10. Science, Laws of Nature, and Causation

In discussing science and causation, Berkeley aims to show that his immaterialism can accommodate, and in some respects clarify, the practices of natural philosophy.

Laws of Nature as Regularities Among Ideas

Berkeley understands laws of nature as descriptions of the regular patterns according to which God orders our sensory ideas. These laws do not reflect inherent powers or necessary connections within material substances but rather:

• Stable rules of divine volition.
• Useful generalizations that enable prediction and control over experience.

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“The laws of nature are nothing else but the established rules of the connection of ideas.”

— Paraphrasing Berkeley’s position in Principles, §§30–31

Scientists, on this view, investigate how ideas are regularly associated, without needing to posit insensible corpuscles or forces existing beyond all possible experience.

Causation: Spirits, Not Bodies

Berkeley denies that bodies or material things possess genuine causal powers. Only spirits—finite minds and God—are truly active. Sensible objects are occasions on which certain ideas appear, but the real cause of their appearance is divine or mental activity.

Some commentators compare Berkeley’s view with occasionalism, which also attributes ultimate causation to God. Others emphasize differences: Berkeley allows for finite spirits to have causal efficacy within the domain of their volitions (e.g., moving their bodies), though dependent on God’s general concurrence.

Science Without Matter

Berkeley repeatedly stresses that his system retains the predictive and mathematical success of Newtonian science. He criticizes the introduction of metaphysical notions such as absolute space, absolute time, or inert matter as unnecessary for scientific practice. Instead, he proposes that scientists focus on correlating observable phenomena (ideas) and expressing these correlations in concise mathematical form.

Critics argue that this view risks reducing science to mere prediction without explanation of underlying mechanisms. Defenders contend that Berkeley anticipates later empiricist and instrumentalist approaches that regard theoretical entities as convenient instruments for organizing experience rather than as literal descriptions of a hidden material reality.

11. Common Sense, Religion, and Practical Life

In §§34–51, Berkeley addresses how his immaterialism relates to everyday belief, religious faith, and practical conduct.

Appeal to Common Sense

Berkeley insists that his doctrine is more in harmony with common sense than materialism. Ordinary people, he claims, take the objects they see and touch to be the very things that exist, without positing a hidden substratum behind appearances. Philosophers, by contrast, introduce matter as something distinct from the sensible qualities and then create skeptical doubts about whether our ideas correspond to it.

He argues that by identifying physical objects with the very ideas we perceive (ordered and sustained by God), his system preserves:

• The reality of tables, trees, and other familiar things.
• The reliability of our senses in guiding action.
• The asymmetry between waking experience and dreams or illusions, based on regularity and coherence.

Critics question whether denying matter truly accords with ordinary thought, which often assumes a world existing independently of any mind. Some interpreters suggest Berkeley is revising rather than simply endorsing common sense.

Religious Implications

Berkeley emphasizes that immaterialism supports a theistic worldview. If the existence and order of nature depend directly on God’s activity, then:

• God’s presence is intimately connected to every aspect of experience.
• There is no self‑sufficient mechanical universe that might encourage deism or atheism.
• The natural world becomes a system of signs by which God communicates ends, warnings, and benefits.

He presents this as safeguarding doctrines of providence and divine conservation. At the same time, he maintains that his philosophy does not conflict with revealed religion but rather removes philosophical obstacles to belief.

Practical Life

Berkeley contends that his view leaves practical life untouched. People may continue to navigate the world, engage in trade, medicine, and mechanical arts, and rely on empirical regularities just as before. The difference lies in the metaphysical interpretation: instead of appealing to inert matter, one acknowledges that all such activities involve interacting with ordered ideas within a divine framework.

Some later commentators see here an anticipation of pragmatic and phenomenological emphases on lived experience; others note tensions between Berkeley’s radical metaphysics and his reassurance that “all goes on as before” in daily practice.

12. Responses to Objections and Clarifications

Sections §§52–84 are largely devoted to answering anticipated objections and refining key claims. Berkeley addresses worries about illusion, error, language, and the alleged paradoxical nature of immaterialism.

Illusion, Error, and Dreaming

One objection holds that if everything perceived is an idea, then illusions and dreams would be as real as waking experience. Berkeley replies by distinguishing:

• Reality: ideas that come to us with great vividness, order, and independence of our will (sensory ideas).
• Imagination or dreams: ideas more faint and irregular, often within our control.

The difference lies not in a relation to matter but in the coherence and steadfastness of ideas.

The Existence of Other Minds

Another concern is that Berkeley’s focus on ideas in one’s own mind might lead to solipsism. He responds by arguing that the regularity and complexity of sensory experience, and the meaningful behavior of other human bodies, provide grounds for inferring the existence of other finite spirits, much as they ground the inference to God as supreme spirit. Critics question the strength of this inference; defenders argue that Berkeley’s position is no more vulnerable than other forms of empiricism.

Language and Meaning

Berkeley clarifies his stance on the meaningful use of physical terms. Terms like “body,” “motion,” or “force” remain legitimate, he claims, so long as they are understood to refer to ideas and their lawful connections rather than to an unknowable substratum. He allows scientific and mathematical language as a system of signs for managing and predicting experiences.

Alleged Self‑Refutation

A further objection charges that Berkeley’s denial of matter is self‑refuting or unimaginable. He answers that the difficulty lies not in his view but in habits of thought formed by long‑standing use of materialist language. Once one reflects carefully on what is genuinely conceived (ideas and spirits), he argues, the notion of matter can be seen as a mere “chimera.”

Commentators continue to debate how adequate these replies are. Some see them as successfully defusing standard criticisms; others think they expose tensions within Berkeley’s attempt to reconcile radical metaphysics with common‑sense and scientific discourse.

13. Reception, Criticisms, and Later Debates

The Treatise’s immediate and long‑term reception has been mixed, ranging from dismissal as paradoxical to recognition as a major contribution to philosophy.

Early Reactions

At the time of publication, the Treatise attracted limited attention. Many contemporaries treated Berkeley’s denial of matter as self‑evidently absurd. Some critics regarded his position as a reductio of empiricism, showing that a consistent application of Lockean principles leads to unacceptable conclusions.

There was, however, more engaged response in certain circles. Samuel Clarke and others in the Newtonian tradition indirectly addressed Berkeleyan themes in debates over space, time, and immaterialism, though not always by name. Berkeley’s own Three Dialogues were partly designed to respond to misunderstandings of the Treatise.

Main Lines of Criticism

Major criticisms that developed over the eighteenth and nineteenth centuries include:

• Solipsism worry: that Berkeley cannot secure the existence of other minds or a robust external world beyond one’s own ideas.
• Dependence on theology: that invoking God as guarantor of the world makes his system rest on contentious religious premises and risks circularity (using experience to prove God, then God to ground experience).
• Threat to mathematics and science: that rejecting abstract ideas undermines general laws, infinitesimals, and counterfactual reasoning.
• Conflict with common sense: that, despite Berkeley’s claims, ordinary belief presupposes a mind‑independent world.

Philosophers such as Thomas Reid criticized Berkeley as an example of how the “theory of ideas” leads to skepticism and idealism, urging a return to a common‑sense realism about external objects.

Later Debates

In the nineteenth century, German idealists and British idealists (e.g., Hegel, T. H. Green, F. H. Bradley) read Berkeley as a precursor, though they often transformed his doctrines significantly. At the same time, empiricist critics treated him as a cautionary example of where certain epistemological assumptions might lead.

The twentieth century saw renewed interest among analytic philosophers. Figures such as Russell and Moore engaged Berkeley critically in formulating their own realist positions, while others explored connections to phenomenalism and the analysis of perception. More sympathetic interpretations, including those of A. A. Luce, Kenneth Winkler, and George Pappas, have argued that many standard objections rest on misunderstandings of his aims and concepts.

Debate continues over how best to situate the Treatise: as primarily a theological apologetic, a radical empiricist metaphysics, a precursor to philosophy of language, or some combination of these.

14. Legacy and Historical Significance

Over time, A Treatise Concerning the Principles of Human Knowledge, Part I has come to be seen as a landmark in the history of philosophy, with enduring influence across several domains.

Impact on Early Modern and Later Thought

Berkeley’s immaterialism shaped subsequent discussions of perception, skepticism, and the mind–world relation. David Hume engaged with Berkeley’s critique of material substance and abstract ideas, though he moved toward a more skeptical, less theistic stance. Kant later acknowledged Berkeley as a significant idealist predecessor, even as he criticized him for allegedly collapsing the distinction between appearance and thing in itself.

In the nineteenth century, the Treatise influenced British idealism, where Berkeley was often cast as an ancestor of more systematic idealist metaphysics. At the same time, he figured in debates about empiricism, with some commentators portraying him as revealing the internal tensions of the “way of ideas.”

Role in Analytic Philosophy and Philosophy of Language

In the early analytic tradition, G. E. Moore and Bertrand Russell used Berkeley as a foil in defending common‑sense realism and logical analysis. However, later analytic philosophers have found in Berkeley anticipations of:

• Phenomenalism: the reduction of talk about physical objects to statements about possible experiences.
• Linguistic analysis: especially his insistence on the clarifying role of examining how terms are used, and his critique of metaphysical pseudo‑ideas grounded in language misuse.

Some see his theory of signs and generality as a precursor to later work on meaning and reference.

Continuing Relevance

Contemporary scholarship often highlights Berkeley’s:

• Challenge to metaphysical realism about material objects.
• Emphasis on the dependence of the physical world on experiential and conceptual frameworks.
• Alternative conception of laws of nature and scientific explanation.

Discussions of idealism, structural realism, and anti‑realist interpretations of science continue to revisit Berkeley’s arguments, either as historical resources or as live options in metaphysical debate.

The Treatise also remains central in histories of empiricism, illustrating how a stringent commitment to experience as the basis of meaning can yield a radically different ontology from that of materialist realism. Whether regarded as a brilliant solution or a provocative challenge, Berkeley’s work continues to shape how philosophers think about the relation between minds, ideas, and the world.