The positive views of the German idealist philosopher Georg Wilhelm Friedrich Hegel (1770–1831) are notoriously difficult, and his epistemology is not susceptible of adequate summary within the scope of this article. Some of his criticisms of earlier epistemological views should be mentioned, however, since they helped to bring the modern era in philosophy to a close.

In his Phenomenology of Spirit (1807), Hegel criticized traditional empiricist epistemology for assuming that at least some of the sensory content of experience is simply “given” to the mind and apprehended directly as it is, without the mediation of concepts. According to Hegel, there is no such thing as direct apprehension, or unmediated knowledge. Although Kant also held that empirical knowledge necessarily involves concepts (as well as the mentally contributed forms of space and time), he nevertheless attributed too large a role to the given, according to Hegel.

Another mistake of earlier epistemological theories—both empiricist and rationalist—is the assumption that knowledge entails a kind of “correspondence” between belief and reality. The search for such a correspondence is logically absurd, Hegel argued, since every such search must end with some belief about whether the correspondence holds, in which case one has not advanced beyond belief. In other words, it is impossible to compare beliefs with reality, because the experience of reality is always mediated by beliefs. One cannot step outside belief altogether. For Hegel, the Kantian distinction between the phenomena of experience and the unknowable thing-in-itself is an instance of that absurdity.

Continental epistemology

In epistemology, Continental philosophers during the first quarter of the 20th century were preoccupied with the problem of overcoming the apparent gap between the knower and the known. If human beings have access only to their own ideas of the world and not to the world itself, how can there be knowledge at all?

The German philosopher Edmund Husserl (1859–1938) thought that the standard epistemological theories of his day lacked insight because they did not focus on objects of knowledge as they are actually experienced by human beings. To emphasize that reorientation of thinking, he adopted the slogan, “To the things themselves.” Philosophers needed to recover a sense of what is given in experience itself, and that could be accomplished only through a careful description of experiential phenomena. Thus, Husserl called his philosophy “phenomenology,” which was to begin as a purely descriptive science and only later to ascend to a theoretical, or “transcendental,” one.

According to Husserl, the philosophies of Descartes and Kant presupposed a gap between the aspiring knower and what is known, one that made claims to knowledge of the external world dubious and in need of justification. Those presuppositions violated Husserl’s belief that philosophy, as the most fundamental science, should be free of presuppositions. Thus, he held that it is illegitimate to assume that there is a problem about our knowledge of the external world prior to conducting a completely presuppositionless investigation of the matter. The device that Husserl used to remove such presuppositions was the epochē (Greek: “withholding” or “suspension”), originally a principle of ancient Greek Skepticism but in Husserl’s philosophy a technique of “bracketing,” or removing from consideration, not only all traditional philosophical theories but also all commonsensical beliefs so that pure phenomenological description can proceed.

The epochē was just one of a series of so-called transcendental reductions that Husserl proposed in order to ensure that he was not presupposing anything. One of those reductions supposedly gave one access to “the transcendental ego,” or “pure consciousness.” Although one might expect phenomenology then to describe the experience or contents of this ego, Husserl instead aimed at “eidetic reduction”—that is, the discovery of the essences of various sorts of ideas, such as redness, surface, or relation. All of those moves were part of Husserl’s project of discovering a perfect methodology for philosophy, one that would ensure absolute certainty.

Husserl’s transcendental ego seemed very much like the Cartesian mind that thinks of a world but has neither direct access to nor certainty of it. Accordingly, Husserl attempted, in Cartesian Meditations (1931), to overcome the apparent gap between the ego and the world—the very thing he had set out to destroy or to bypass in earlier works. Because the transcendental ego seems to be the only genuinely existent consciousness, Husserl also was faced with the task of overcoming the problem of solipsism.

Many of Husserl’s followers, including his most famous student, Martin Heidegger (1889–1976), recognized that something had gone radically wrong with the original direction of phenomenology. According to Heidegger’s diagnosis, the root of the problem was Husserl’s assumption that there is an “Archimedean point” of human knowledge. But there is no such ego detached from the world and filled with ideas or representations, according to Heidegger. In Being and Time (1927), Heidegger returned to the original formulation of the phenomenological project as a return to the things themselves. Thus, in Heidegger’s approach, all transcendental reductions are abandoned. What he claimed to discover is that human beings are inherently world-bound. The world does not need to be derived; it is presupposed by human experience. In their prereflective experience, humans inhabit a sociocultural environment in which the primordial kind of cognition is practical and communal, not theoretical or individual (“egoistic”). Human beings interact with the things of their everyday world (Lebenswelt) as a workman interacts with his tools; they hardly ever approach the world as a philosopher or scientist would. The theoretical knowledge of a philosopher is a derivative and specialized form of cognition, and the major mistake of epistemology from Descartes to Kant to Husserl was to treat philosophical knowledge as a paradigm of all knowledge.

Notwithstanding Heidegger’s insistence that a human being is something that inhabits a world, he marked out human reality as ontologically special. He called that reality Dasein—the being, apart from all others, which is “present” to the world. Thus, as in Husserl’s phenomenology, a cognitive being takes pride of place in Heidegger’s philosophy.

In France the principal representative of phenomenology in the mid-20th century was Maurice Merleau-Ponty (1908–61). Merleau-Ponty rejected Husserl’s bracketing of the world, arguing that human experience of the world is primary, a view he encapsulated in the phrase “the primacy of perception.” He furthermore held that dualistic analyses of knowledge, best exemplified by traditional Cartesian mind-body dualism, are inadequate. In fact, in his view, no conceptualization of the world can be complete. Because human cognitive experience requires a body and the body a position in space, human experience is necessarily perspectival and thus incomplete. Although humans experience a material being as a multidimensional object, part of the object always exceeds their cognitive grasp just because of their limited perspective. In Phenomenology of Perception (1945), Merleau-Ponty developed those ideas, along with a detailed attack on the sense-datum theory (see below Perception and knowledge).

The epistemological views of Jean-Paul Sartre (1905–80) are similar in some respects to those of Merleau-Ponty. Both philosophers rejected Husserl’s transcendental reductions and both thought of human reality as “being-in-the-world,” but Sartre’s views have Cartesian elements that were anathema to Merleau-Ponty. Sartre distinguished between two basic kinds of being. Being-in-itself (en soi) is the inert and determinate world of nonhuman existence. Over and against it is being-for-itself (pour soi), which is the pure consciousness that defines human reality.

Later Continental philosophers attacked the entire philosophical tradition from Descartes to the 20th century for its explicit or implicit dualisms. Being/nonbeing, mind/body, knower/known, ego/world, being-in-itself/being-for-itself are all variations of a pattern of thinking that the philosophers of the last third of the 20th century tried to undermine. The structuralist Michel Foucault (1926–84), for example, wrote extensive historical studies, most notably The Archaeology of Knowledge (1969), in an attempt to demonstrate that all concepts are historically conditioned and that many of the most important ones serve the political function of controlling people rather than any purely cognitive purpose. Jacques Derrida (1930–2004) claimed that all dualisms are value-laden and indefensible. His technique of deconstruction aimed to show that every philosophical dichotomy is incoherent because whatever can be said about one term of the dichotomy can also be said of the other.

Dissatisfaction with the Cartesian philosophical tradition can also be found in the United States. The American pragmatist John Dewey (1859–1952) directly challenged the idea that knowledge is primarily theoretical. Experience, he argued, consists of an interaction between living beings and their environment. Knowledge is not a fixed apprehension of something but a process of acting and being acted upon. Richard Rorty (1931–2007) did much to reconcile Continental and analytic philosophy. He argued that Dewey, Heidegger, and Ludwig Wittgenstein were the three greatest philosophers of the 20th century specifically because of their attacks on the epistemological tradition of modern philosophy.

Analytic epistemology

Analytic philosophy, the prevailing form of philosophy in the Anglo-American world since the beginning of the 20th century, has its origins in symbolic logic (or formal logic) on the one hand and in British empiricism on the other. Some of its most important contributions have been made in areas other than epistemology, though its epistemological contributions also have been of the first order. Its main characteristics have been the avoidance of system building and a commitment to detailed, piecemeal analyses of specific issues. Within that tradition there have been two main approaches: a formal style deriving from logic and an informal style emphasizing ordinary language. Among those identified with the first method are Gottlob Frege (1848–1925), Bertrand Russell (1872–1970), Rudolf Carnap (1891–1970), Alfred Tarski (1902–83), and W.V.O. Quine (1908–2000), and among those identified with the second are G.E. Moore (1873–1958), Gilbert Ryle (1900–76), J.L. Austin (1911–60), Norman Malcolm (1911–90), P.F. Strawson (1919–2006), and Zeno Vendler (1921–2004). Ludwig Wittgenstein (1889–1951) can be situated in both groups—his early work, including the Tractatus Logico-Philosophicus (1921), belonging to the former tradition and his later work, including the posthumously published Philosophical Investigations (1953) and On Certainty (1969), to the latter.

Perhaps the most distinctive feature of analytic philosophy is its emphasis on the role that language plays in the creation and resolution of philosophical problems. Those problems, it is said, arise through misunderstandings of the forms and uses of everyday language. Wittgenstein said in that connection, “Philosophy is a battle against the bewitchment of the intelligence by means of language.” The adoption at the beginning of the 20th century of the idea that philosophical problems are in some important sense linguistic (or conceptual), a hallmark of the analytic approach, has been called the “linguistic turn.”

Commonsense philosophy, logical positivism, and naturalized epistemology

Three of the most-notable schools of thought in analytic philosophy are commonsense philosophy, logical positivism, and naturalized epistemology. Commonsense philosophy is the name given to the epistemological views of Moore, who attempted to defend what he called the “commonsense” view of the world against both skepticism and idealism. That view, according to Moore, comprises a number of propositions—such as the propositions that Earth exists, that it is very old, and that other persons now exist on it—that virtually everybody knows with certainty to be true. Any philosophical theory that runs counter to the commonsense view, therefore, can be rejected out of hand as mistaken. Into that category fall all forms of skepticism and idealism. Wittgenstein also rejected skepticism and idealism, though for very different reasons. For him, those positions are based on simplistic misunderstandings of epistemic concepts, misunderstandings that arise from a failure to recognize the rich variety of ways in which epistemic terms (including words such as belief, knowledge, certainty, justification, and doubt) are used in everyday situations. In On Certainty, Wittgenstein contrasted the concepts of certainty and knowledge, arguing that certainty is not a “surer” form of knowledge but the necessary backdrop against which the “language games” of knowing, doubting, and inquiring take place. As that which “stands fast for all of us,” certitude is ultimately a kind of action: “Action lies at the bottom of the language game.”

The doctrines associated with logical positivism (also called logical empiricism) were developed originally in the 1920s and ’30s by a group of philosophers and scientists known as the Vienna Circle. Logical positivism became one of the dominant schools of philosophy in England with the publication in 1936 of Language, Truth, and Logic by A.J. Ayer (1910–89). Among the most influential theses put forward by the logical positivists was the claim that in order for a proposition with empirical content—i.e., one that purports to say something about the world—to be meaningful, or cognitively significant, it must be possible, at least in principle, to verify the proposition through experience. Because many of the utterances of traditional philosophy (especially metaphysical utterances, such as “God exists”) are not empirically verifiable even in principle, they are, according to the logical positivists, literally nonsense. In their view, the only legitimate function of philosophy is conceptual analysis—i.e., the logical clarification of concepts, especially those associated with natural science (e.g., probability and causality).

In his 1950 essay “Two Dogmas of Empiricism,” Quine launched an attack upon the traditional distinction between analytic statements, which were said to be true by virtue of the meanings of the terms they contain, and synthetic statements, which were supposed to be true (or false) by virtue of certain facts about the world. He argued powerfully that the difference is one of degree rather than kind. In a later work, Word and Object (1960), Quine developed a doctrine known as naturalized epistemology. According to that view, epistemology has no normative function. That is, it does not tell people what they ought to believe. Instead, its only legitimate role is to describe the way knowledge, especially scientific knowledge, is actually obtained. In effect, its function is to describe how present science arrives at the beliefs accepted by the scientific community.