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5.1: Three Theories of Knowledge

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    Language Overview

    Before we look into the various theories about how we know what we know when we make propositional claims and how to determine if claims are true or not it would be helpful to make a number of important points or distinctions about language and how we use it. Not all uses of language involve a claim that can be described as claims of knowledge. There are a variety of forms of expressions or sentences in any language. Not all sentences are functioning for the speaker in the same way.

    Language Claims

    Here are five of the different uses for language:

    Expressive (this use includes sentences that are neither true nor false). They express the feelings of the speaker/writer.

    • holy cow!
    • ouch
    • hooray!

    Directive (thus use includes sentences that are neither true nor false). This use offers instructions or requests information.

    • please close the door
    • what time is it?
    • how much does that cost?

    Performative (thus use includes sentences that are neither true nor false). This use actually performs some operation. It presents no information and makes no requests.

    • I bid five dollars
    • I promise that i will do that
    • I now pronounce you ...

    Evaluative (thus use includes sentences that are neither true nor false). This use expresses how people think about some object, activity, person, condition, or situation.

    • That is a good car
    • She is a good person
    • Chocolate is the best flavor for ice cream.

    As the standard for making such evaluations is not such as to be derived from a source that is recognized as existing apart from humans and uninfluenced by culture there is no commonly agreed upon method for determining if such evaluations are true or not true. Sentences expressing evaluations are not taken as making claims about what is known so much as making claims about how the evaluator thinks.

    Cognitive (this use includes sentences that are either true or false, or potentially true or false). It is the cognitive use of language that concerns us with the issue of knowledge.

    • There are three sides to a triangle. The sum of their angles is 180 degrees.
    • There is a computer in front of you right now.
    • 23 + 11= 34
    • A bachelor is an unmarried male.
    • If a is more than b, and b is more than c, then a is more than c.
    • There are 1.8376 x 1073 grains of sand on planet earth.

    This is the use involved with propositional knowledge. It is the cognitive use that makes claims that should be capable of being determined to be either true or false. Cognitive use of language expressing that which is claimed as knowledge exists in a variety of forms: logical, semantic, systemic, and empirical. We will examine them in a subsequent section. What they have in common is that claims are made that can be determined to be true or false in some manner or other.


    Rationalism is a reliance on reason {lat. ratio} as the only reliable source of human knowledge. In the most general application, rationalism offers a naturalistic alternative to appeals to religious accounts of human nature and conduct. A psychological characterization of rationalism would describe it as an overly deductive way of thinking and to the molding of reality to fit one's theoretical understanding. More specifically, rationalism is the epistemological theory that significant knowledge of the world can best be achieved by a priori means; it therefore stands in contrast to empiricism.

    The first philosophers who are today referred to as having been rationalists include Descartes (1596-1650), Leibniz (1646-1716), and Spinoza (1632-1677). These thinkers thought they were defending a form of rational thought in the form of a science, against the older school of thought known as scholasticism. The defense of science offered by Descartes included a form of dualism that carried over elements of tradition of the scholastic's in a form of thinking that is technical, deductive, and abstract. In Spinoza's Ethics, the method is again deductive and modeled on the geometric system of Euclid's Elements. Rationalism is a method of thinking that is marked by a deductive and abstract way of reasoning.

    Baruch Spinoza

    In ordinary usage, Rationalism is a basic sense of respect for reason or refers to the idea that reason should play a large role in human life (in contrast, say, to mysticism). So with rationalism it is possible to have knowledge without having sensory experiences. There is knowledge of logic and its laws or rules that are based upon reasoning and not sensory experience. There is a knowledge that is innate or born inside of us, that is to say that there are forms of knowledge that exists within our minds from the time we are born.

    For Descartes knowledge involves certainty and certainty exists in the form of clear and distinct ideas, which are ideas that are indubitable (not capable of being doubted). These would be innate ideas that all rational beings are born with such as; knowledge of self, God, and the world. But all knowledge is the result of acts of reasoning.

    Rene Descartes

    Leibniz distinguished the truths of reasoning which were necessary truths as in the rule of contradictions, and excluded middle (statements are either true or false) from the truths of fact which are not necessary but are contingent upon experience and sufficient reason needed to accept what the senses report. The work of Leibniz anticipated modern logic and analytic philosophy, but his philosophy also looks back to the scholastic tradition, in which conclusions are produced by applying reason to first principles or prior definitions rather than to empirical evidence.


    Reliance on experience as the source of ideas and knowledge. More specifically, empiricism is the epistemological theory that genuine information about the world must be acquired by a priori means, so that nothing can be thought without first being sensed. Prominent modern empiricists include Bacon, Locke, Berkeley, Hume, and Mill. In the twentieth century, empiricism principles were extended and applied by the pragmatists and the logical positivists.

    Empiricism is a theory that states that knowledge comes only or primarily from sensory experience. It is one of several views of epistemology, the study of human knowledge, along with rationalism and skepticism. Empiricism emphasizes the role of empirical evidence in the formation of ideas, over the idea of innate ideas or traditional empiricists may argue however that traditions (or customs) arise due to relations of previous sense experiences.

    Empiricism in the philosophy of science emphasizes evidence, especially as discovered in experiments. It is a fundamental part of the scientific method that all hypotheses and theories must be tested against observations of the natural world rather than resting solely on a priori reasoning, intuition, or revelation.

    Empiricism, often used by natural scientists, says that "knowledge is based on experience" and that "knowledge is tentative and probabilistic, subject to continued revision and falsification.


    John Locke

    For Locke the mind is a blank slate at birth (tabula rasa) and all knowledge results from experiences that enter the mind from the experiences of the body. Knowledge of ideas is possible because ideas are representations of things experienced. But if representations are copies of our experiences, just how accurate are they?

    Locke distinguished the primary and secondary qualities of an object of an experience and opened a door to a major problem in determining just how accurate sense knowledge could ever be. Locke distinguished the properties that where in or with the object and those that existed within the mind of the subject of the experience. The object has a texture but the idea of “smoothness” is in the subject. The object had a degree of heat but “hot” and “cold” are ideas in the knower.

    John Locke on Epistemology

    David Hume

    Hume was a skeptic. He agreed with Locke that we are born with a blank slate, tabla rasa and that all our knowledge comes through the senses (empiricism), but he did not think that we could know all that much for certain. (skepticism). He held that are perceptions are or make impressions which are our thought, that we have no ideas without sense impressions, that reasoning (a priori) does not lead to knowledge, that sense impressions are not proof of an external independent reality.

    Empiricism (David Hume)

    Problems with Empiricism

    The empiricists could not overcome problems with accounting for forms of knowledge that did not relate to the senses, e.g., in mathematics and in logic. And they could not account for how it could be that humans can have knowledge for which there is no direct experience, for example of the universe as a whole or of subatomic events or quanta of energy, entities for which there can be no direct experience.

    The Epistemological Theory of Immanuel Kant

    For Kant there is:

    • Unity of consciousness
    • Unity of being
    • Unifying act of the mind

    To account for this and our relation to being, Kant postulates that there must exist rules for thoughts, which he calls categories that are innate and necessary for understanding. Without such rules operating there is no way to account for our knowledge of such ideas as:

    • substance
    • space
    • time
    • unity
    • plurality
    • cause and effect
    • possibility
    • necessity
    • reality

    Knowledge has both form and content.

    1. form or structure of knowledge of reality-
      1. reason
      2. categories
      3. part of the way in which the mind operates
    2. content of the knowledge of reality
      1. provided through the senses

    So, ideas constitute our experience but, there is a fundamental distinction to be made of two types of knowledge

    1. Knowledge of the thing as it appears through our senses as filtered by the brain-phenomena
      1. This is possible and what we generally call knowledge of the world
    2. Knowledge of the thing as it is in itself noumena
      1. a thing as it is in itself

    This is not possible for humans can never get beyond or away from the categories of the understanding which shape and influence all that the human experiences because humans can never think without using the mind-brain and thus involving its structure and manner of operating.

    For Kant humans will never know things as they are in themselves because humans can never think without their brains and the brains are so structured as to provide for arrangements and ordering and connecting elements for human thought to occur. It is as if the humans must always see things through colored glasses because they cannot remove them. Therefore the universe will always appear through the tinting of those glasses. Humans will never know how the universe actually looks. Humans may get close, but can not experience the thing itself directly. How do we acquire ideas?

    Kant combines ideas of the rationalists and the empiricists.

    Rationalism Empiricism
    innate empirical
    a priori from experience

    How is knowledge organized in the mind? The mind introduces new principles of order into experience and arranges, stores and tests arrangements and then tests the efficacy of those ideas and arrangements.

    Transcendental idealism

    all propositions are a priori empirical

    analytic syntheti

    1. Analytic a priori: e.g. Math, definitions
    2. Analytic empirical: don't exist
    3. Synthetic a priori: categories, rules, principles
      1. part of perception
      2. part of thought
    4. Synthetic empirical: all physical claims - this includes all of the sciences.

    Kant's Theory of Epistemology

    Kant’s contributions of the distinction of types of knowledge and of the role played by the order of the brain remain a dominating influence over thinking about epistemological issues to this day.

    Immanuel Kant is considered to be one of the world's greatest philosophers. In his account of epistemological theory of knowledge, called transcendental idealism, he claimed that “the mind of the knower makes an active contribution to experience of objects before us”. He meant that whatever we already know through our experience makes it easier for us to acquire new means of knowledge.

    Accordingly, Kant specified two sources of our knowledge, which are the mind’s receptive capacity (sensibility), and the mind’s conceptual capacity (understanding). He thought that it would be impossible for people to have any experience of objects, which are not placed in space and time. These conditions of sensibility are due to our consciousness, which must “apprehend objects as occupying a region of space and persisting for some duration of time”.

    However, sensibility by itself doesn’t make judging objects possible. According to empirical derivation, it also takes understanding, which provides the concepts, the rules for determining what is “common or universal in different representations”. He said, “without sensibility no object would be given to us; and without understanding no object would be thought. Thoughts without content are empty; intuitions without concepts are blind”. He meant that in order to think about some object it takes understanding, which assigns concepts, based on the object’s sensation input, to identify what is common and general about it.

    Nevertheless, empirical derivation discussed above is not sufficient to explain all of the concepts that arise in the human life, such as causation, substance, self, identity, space, time, etc. It’s due to the fact that these concepts are products of our experience, which is constituted by ideas. Therefore, “Kant postulates that there must exist rules for thoughts, which he calls categories that are innate and necessary for understanding” all of the concepts. In addition to mind’s conceptual contribution to experience only that special set of concepts organized into these fundamental categories of thought make empirical concepts and judgments possible.

    Although these concepts cannot be experienced directly, they are present when particular judgments of objects take place. Plus, “since objects can only be experienced spatio-temporally, the only application of concepts that yields knowledge is to the" Kant rejects any kind of knowledge that goes beyond the bounds of sensation because there can be no objects for the understanding to judge, rightly or wrongly. While Kant is a transcendental idealist he believes the nature of objects as they are in themselves is unknowable to us.

    However, the knowledge of appearance is...possible. Therefore, knowledge of the things can never get beyond the categories of understanding, which shape and influence all that the human experiences. Accordingly, human will never know how the universe actually looks because they aren’t able to think without any arrangement and order of elements. Kant’s theory of knowledge combines rationalism and the empiricism in his account to distinct types of knowledge and the principles of mind‘s order.


    Skepticism is the belief that some or all human knowledge is impossible. Since even our best methods for learning about the world sometimes fall short of perfect certainty, skeptics argue, it is better to suspend belief than to rely on the dubitable products of reason. Classical skeptics include Pyrrho and Sextus Empiricus. In the modern era, Montaigne, Mayle, and Hume all advocated some form of skeptical philosophy. Fallibilism is a more moderate response to the lack of certainty.

    The Problem of Skepticism

    A degree of skepticism is quite healthy as a counterpoint to being too credulous and being taken in by poor reasoning and illusions or deliberate attempts to mislead and deceive. Skepticism holds that it is not possible to have knowledge is self-defeating and not productive. There should be a skeptical inquiry that is used before humans reach conclusions and decide which beliefs they will hold. There is a sort of positive skepticism that urges caution and all deliberate care and critique before drawing conclusions or setting beliefs but does not reject the possibility of either achieving knowledge or gaining closer proximity to knowledge and truth.

    Philosophical Applications

    1. How much and what type of evidence or support is needed to warrant a claim to know something?

    NOTE: Different types of knowledge would require different types of support. What would be needed and how much to prove a claim to know something?

    1. Is truth relative, or a matter of opinion?

    Read the following quote and answer the question.

    “How often has it happened to me that in the night I dreamt that I found myself in this particular place…while in reality I was lying in bed.”

    1. Can you be certain that you’re not dreaming right now? If so, how?

    Vocabulary Quizlet 5.1

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