Epistemology is the branch of philosophy that investigates the basic nature of knowledge, including its sources and validation. Epistemology is concerned with the basic relationship between man's mind and reality, and with the basic operations of human reason. It therefore sets the standards for the validation of all knowledge; it is the fundamental arbiter of cognitive method.

The major issues in epistemology can be classified into five topic areas:

  • The fundamental relationship between consciousness and reality;
  • The nature and validity of sense-perception;
  • The nature of concepts and the relation between abstractions and concrete particulars;
  • The nature and validation of axioms, especially the laws of identity and causality;
  • The nature of certainty and truth as characteristics of conceptual knowledge.

Objectivism has a unique perspective in each of these areas, though its approach is more fully developed in some areas than in others. Leonard Peikoff's Objectivism: The Philosophy of Ayn Rand, chapters 1-5, is the only systematic presentation of the Objectivist epistemology as a whole. Though Peikoff's discussion is flawed in certain respects (see "Peikoff's Summa," by David Kelley, IOS Journal, I, #3), it is worth consulting on all the topics listed above.

To understand the full meaning and significance of the Objectivist epistemology, one must have a broader grasp of the issues it addresses, and of the rival theories about those issues. The purpose of this Study Guide is to suggest readings that provide a useful introduction to the major issues and theories in each area, as well as works that present the Objectivist position.


Epistemological issues have been discussed throughout the history of philosophy. Among the ancient Greeks, questions of knowledge were raised by Plato and Aristotle, as well as by the Sophists and the Sceptics, and many of the chief issues, positions and arguments were explored at this time. In the systems of Plato and Aristotle, however, epistemological questions were largely subordinated to metaphysical ones, and epistemology did not emerge as a distinct area of inquiry.

The scholastics of the late medieval period were especially concerned with two epistemological questions: the relationship between reason and faith, and the nature of concepts and universals. The major positions on the latter issue—realism, nominalism, and conceptualism—were defined during this period.
The Reformation and the rise of modern science raised questions about cognitive methodology, and gave rise to a rebirth of skeptical doctrines, trends that culminated in the writings of René Descartes (1596-1650).
During the modern period, from Descartes to Immanuel Kant (1724-1804), epistemological concerns were at the forefront of philosophy, as thinkers attempted to understand the implications of the new science. They also attempted, unsuccessfully, to deal with skeptical attacks on the validity of sense perception, concepts, and induction. In the 19th and 20th centuries, epistemological issues continued to receive attention from philosophers of various schools, including Idealism, Logical Positivism, and Linguistic Analysis.
A familiarity with the history of philosophy provides the best introduction to epistemology. The following works are of special importance for epistemology:
  • Plato, Theaetetus
  • Aristotle, Posterior Analytics
  • René Descartes, Meditations
  • John Locke, Essay Concerning Human Understanding
  • David Hume, An Inquiry Concerning Human Understanding
  • Immanuel Kant, Prolegomena to Any Future Metaphysics

These works are available in many editions. Locke's two-volume Essay is by far the longest, and an abridged version is suggested.

An overview of the field may be found in The Encyclopedia of Philosophy entry, "Epistemology, History of," by D. W. Hamlyn. This article omits certain important points, and the material it does contain is not always selected or integrated on the basis of essentials. But it does cover most of the major thinkers and issues, and provides a sense of continuity from the Greeks to the 20th century. Nicholas Capaldi's Human Knowledge is an engaging non-historical introduction to most of the central issues in epistemology; his discussion of skepticism is particularly good.

Consciousness and Reality

The fundamental issue in epistemology concerns the relationship between consciousness and reality, the knower and the known. Objectivism maintains that existence exists independently of consciousness, and that the mind's function is to grasp the identity of what exists. This position, known as realism, or the primacy of existence, is opposed to idealism, or the primacy of consciousness, which holds that the objects of knowledge are dependent in some way on the knower—that reality is constituted by or relative to our own minds.
The Objectivist position and its validation are presented in David Kelley's The Evidence of the Senses, Chapters 1 and 6, which also describe Objectivism's unique understanding of objectivity. The realist position is also defended in Roger Trigg's Reason and Commitment. Though Trigg's approach is not consistent with Objectivism in all respects, his book is a thorough review of the ways in which the idealist position is self- refuting.


Objectivism subscribes to the thesis of empiricism: that sense perception is our basic form of contact with reality, and that all knowledge rests on perceptual evidence. The Objectivist viewpoint on perception, however, is unique in a number of respects. The most important is its rejection of the representationalist view that we perceive external objects indirectly, through the medium of images or representations internal to consciousness. The representationalist view, which dominated modern philosophy and is still commonly accepted, arose from the fact that the appearance of an object is partly dependent on the nature and operations of our sensory systems.
Objectivism offers a radically new theory of perceptual appearances as forms in which we perceive objects directly. Kelley's Evidence of the Senses provides a detailed account of this theory, along with the Objectivist position on the other major issues regarding perception, including the validity of the senses, the relation between sensation and perception, and the validation of perceptual judgments by direct perceptual awareness.
Philosophical and psychological issues are intimately related in the study of perception. Philosophers frequently appeal to psychological theories, and those theories in turn often reflect implicit philosophical assumptions. The psychological approach most congruent with Objectivism is that pioneered by the late James J. Gibson, whose Ecological Approach to Visual Perception was his final word on the subject.


"The issue of concepts," Ayn Rand observed in Introduction to Objectivist Epistemology, the one systematic philosophical treatise she wrote,
is philosophy's central issue. Since man's knowledge is gained and held in conceptual form, the validity of man's knowledge depends on the validity of concepts. But concepts are abstractions or universals, and everything that man perceives is particular, concrete. What is the relationship between abstractions and concretes? To what precisely do concepts refer in reality?
Rand's treatise presents an original theory of the process of forming concepts, and goes on to derive the implications of the theory for a number of issues, including the relationship between abstractions and concretes, the nature of definitions, the role and validation of axioms, and the nature of objectivity. The final chapter contains Rand's fullest discussion in print of the crucial distinctions among the intrinsic, the subjective, and the objective. The expanded second edition of this work also contains transcripts of a workshop in which she discussed a wide range of other issues. David Kelley's essay "A Theory of Abstraction" is a detailed commentary on Rand's theory and its relationship to other theories.
The importance of the problem of universals has been recognized throughout the history of Western philosophy. Hilary Staniland's The Problem of Universals is an excellent introduction to the issues, reviewing the major theories from Plato to Wittgenstein; it provides a useful way to gain an understanding of the novelty and significance of the Objectivist viewpoint. Richard Aaron's Universals describes the rejection of realism by the British empiricists and discusses the problems of their own nominalist positions. It is an excellent survey of the problems that Rand's theory addresses.
Some recent philosophers, including Saul Kripke and Hilary Putnam, have challenged the conventional nominalist view that the cognitive content of a concept consists in a stipulated meaning or definition. On their view, which is consistent with Objectivist in many (but not all) respects, a concept designates a kind of thing in reality and includes in its content the properties such things actually have; defining traits are discovered, not stipulated. The issues in this controversy are discussed in Naming, Necessity, and Natural Kinds, edited by Stephen P. Schwartz. Schwartz's "Introduction" is particularly worth reading, as is the essay by Irving Copi on essences.


The vast bulk of our knowledge is derived by reasoning from the data provided by our senses. Deductive reasoning relies on the law of noncontradiction; inductive reasoning relies on the law of causality. The objectivity of our knowledge therefore depends on the validation of these laws. Readings in Logic, edited by Irving Copi and James Gould, contains selections from classical and modern philosophers, representing the major positions on this issue.
Since the time of Hume, most philosophers have held that the law of noncontradiction, and the related laws of identity and excluded middle, are true by convention. This view is most clearly expressed in the title essay of Logic Without Metaphysics, by Ernest Nagel. Objectivism sides with the realist minority, which holds that the laws have ontological import—that they state general facts about the world. The major arguments for this position may be found in Chapter 10 of Brand Blanshard's Reason and Analysis. (The book as a whole is an excellent critique of logical positivism and ordinary language philosophy).
The law of causality, which states that the same cause must have the same effect, lies at the crux of the problem of induction first posed by Hume. An excellent discussion of the law and its validation may be found in An Introduction to Logic, by H.W.B. Joseph, Chapter 19.
The epistemological issues regarding induction are intimately related to metaphysical issues about the nature of causality. Causal Powers, by Rom Harré and Edward Madden, is a penetrating modern defense of the Aristotelian conception of causality, as against the Humean. Though the authors' distinction between conceptual and natural necessity is not consistent with the Objectivist view of concepts, their discussion of the necessity of causal relationships is excellent.

Certainty and Truth

Certainty and truth are epistemological concepts identifying the basic standards of objectivity. According to Objectivism , both concepts designate the grasp of facts at the conceptual level. The concept of truth is required by the possibility of error; an assertion is true if it corresponds to reality, false if it does not. The concept of certainty is required by the fact that evidence comes in degrees; an assertion is certain if it is fully supported by the evidence; where the evidence is incomplete, the proposition may be possible or probable.
Objectivism holds that both truth and certainty must be defined in terms of a specific context of knowledge. In particular, it rejects the common assumption that certainty requires infallibility. The contextual theory is summarized in Peikoff's Objectivism, Chapters 4-5, where the theory is derived from the view of abstractions as objective rather than intrinsic or subjective. No Objectivist philosopher, however, has yet produced a complete formulation of the theory that deals adequately with all the traditional problems.
Objectivism is in basic agreement with the classical understanding of truth as correspondence to the facts. D. J. O'Connor's The Correspondence Theory of Truth is an excellent introduction to this theory and its rivals, both classical and contemporary. The book poses a number of theoretical issues that remain to be solved.


Richard Aaron. Universals. Oxford: Clarendon Press, 1952.

Brand Blanshard. Reason and Analysis. LaSalle: Open Court Publishing Co., 1964.

Nicholas Capaldi. Human Knowledge. New York: Western Publishing Co., 1969.

Irving M. Copi and James A. Gould. Readings in Logic, 2nd ed. New York: Macmillan Co., 1972.

James J. Gibson. Ecological Approach to Visual Perception. Boston: Appleton-Century-Crofts, 1979.

D.W. Hamlyn. "Epistemology, History of," The Encyclopedia of Philosophy.

Rom Harré and Edward Madden. Causal Powers. Totowa, N.J.: Rowman and Littlefield, 1975.

H.W.B. Joseph. An Introduction to Logic. Oxford: Oxford University Press, 1967.

David Kelley. The Evidence of the Senses. Baton Rouge and London: Louisiana State University Press, 1986.

David Kelley. "A Theory of Abstraction," Cognition and Brain Theory, Volume 7, 1984. Reprinted by the Institute for Objectivist Studies, 1994.

Ernest Nagel. Logic Without Metaphysics. Glencoe, Ill.: Free Press, 1957.

D.J. O'Connor. The Correspondence Theory of Truth. London: Hutchinson University Library, 1975.

Leonard Peikoff. Objectivism: The Philosophy of Ayn Rand. New York: Penguin Group, 1991.

Ayn Rand. Introduction to Objectivist Epistemology, expanded 2nd ed. New York: Penguin Group, 1990.

Stephen P. Schwartz. Naming, Necessity, and Natural Kinds. Ithaca, NY: Cornell University Press, 1977.

Hilary Staniland. The Problem of Universals. Garden City: Doubleday & Co., 1972.

Roger Trigg. Reason and Commitment. Cambridge: Cambridge University Press, 1973.

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David Kelley

About The Author:

Author: David Kelley
David Kelley is the founder and executive director of The Atlas Society. A professional philosopher, teacher, and best-selling author, he has been a leading proponent of Objectivism for more than 25 years.

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