Unit 3: Epistemology

An Introduction to Western Epistemology

Heather Wilburn, Ph.D.

The overall problem of epistemology is the attempt to get at the difference between how things appear to us and how things actually are. It seems we know the appearance of things in that we know the colors of an object, how an object feels, what it tastes like, and so forth. Still, all of these things that we know are based on our sense organs; we see the color blue, we feel smoothness, and we taste tartness. It seems that all of these qualities are in relation to us as perceivers. So, what can we say about the object itself? Bertrand Russell explores this question in The Problems of Philosophy.

Russell: The Problems of Philosophy

In our search for certainty and knowledge it is natural to begin with our experiences and then make inferences about what is or is not the case based on those experiences. However, Russell points out that many of the things that we assume to be true—many of the things that we take for granted—can really be doubted.

For example, if another person comes into the room, barring a lack of a specific sense organ, I expect that person to see and experience the same things I am currently experiencing. I expect others to experience the walls as white, the tables as brown, my water bottle as orange, and so forth. We expect other people with the same sense faculties to have the same experiences.

Russell shows why these kinds of assumptions are ungrounded and can be doubted. He claims that the “real” shape or color is not what we see; it is something that is inferred from what we see. What we see is constantly changing. For example, the lighting in the room can make the object appear darker or lighter. The position I occupy in the room can make the object appear less or more square. The tint of my glasses can make the object appear rose-colored or blue. Thus, the senses do not give us truth about the table itself, but only about the appearance of the table or about how we experience the table.

The real table, if there is one, is not immediately known to us. Two difficulties arise: 1) Is there a real table at all and 2) if so, what kind of object can it be?

This is the problem of knowledge: perhaps we know the appearances of things, but how can we know that we really know the reality “behind” them?

Russell’s discussion sets up the main problem of epistemology in the west. Although these questions were taken up by thinkers in ancient times, over the course of time and through the period of modernity.

There are two ways to main approaches to epistemology:

Rationalism: human reason can give us knowledge of reality

Empiricism: this view holds that experience is the source of all knowledge; knowledge is derived from sense experience. As John Locke claimed, the mind is a tabula rasa (i.e. a blank slate).

While this debate became formalized in modern philosophy in the west, the problem itself was laid out by Plato in his dialogue, Theatetus.

The character Theatetus is an empiricist; he holds that knowledge is based on perception—on sense experience.

Socrates shows this view to be problematic because one person can experience something in one way while another person can experience it in another. When it is windy, I am chilly and you are not.

If knowledge is based on sense experience, this would lead us to the absurd claim that the wind is both cold and not cold. An object, then, is not just one thing. Since this is an absurd claim the empiricists cannot have any knowledge at all.

Socrates concludes that knowledge must be something other than perception and it is reason that is the true source of knowledge. In the modern period, this approach to epistemology is adopted by Descartes.


Descartes wanted to move from doubt to knowledge and certainty. So, his doubt is not simply a mode of skepticism, but, rather, it is to enable him to separate what is doubtful from what is not doubtful. He was seeking “clear and distinct” ideas, which could not be doubted. Once he finds one clear and distinct idea he can use it as a premise from which to deduce other beliefs about reality.

Recall the fallibility of our senses. From the examples we’ve been discussing to the problems that Russell pointed out: If we can be mistaken about something as simple and certain as color, it seems likely that we could be mistaken about all kinds of things that are based on our perceptions.

In his Meditations, Descartes delivers six meditations that begin with his resolve to doubt everything that he believes until he can find that one belief that just cannot be doubted. In Meditation 1, he states his method and then begins to eliminate beliefs about which he could be mistaken.

For the sake of the sciences, Descrates believes he must build a firm foundation for knowledge. In order to do this he must rid himself of all of his previous opinions. Now he is not going to go through each belief individually. Instead, he wants to systematically doubt his beliefs by breaking them down into categories.

The first set of beliefs are common sense beliefs that rest on the senses. Despite our reliance on our senses, we can be deceived by them.

Descartes continues: even though there are errors based on our senses, it seems likely that we can at least recognize that we are sitting in this workspace, dressed in certain clothing, writing our philosophical notes on these pages of paper, and the like. How can I deny that this body is mine?

The next category of faulty beliefs come from the possible experience of confusing one’s waking state and dreaming state. Descartes explains, given he is a man who sleeps and dreams, he could be confusing his awake life with a dream. I appear to be doing all of these philosophical and academic activities, but I could simply be dreaming.

At this level of doubt, he doubts the existence of the whole of physical nature, even his own physical body. After all, one dreams about physical nature, so it seems that he can doubt whether his body and the external word exists. The film, The Matrix gives a visual representation of this idea with its emphasis on the mind and plugging in.

Next, Descartes thinks that the principles of mathematics should be certain. However, these too can be doubted. It seems that God could deceive him–tricking him into misunderstanding mathematical functions. He wonders, how can I be certain that an all-powerful God has not deceived me into thinking that the physical world exists or that 2+2=4.

However, Descartes actually argues that God could not have done this. Why not? Remember, Descartes is writing shortly after Galileo’s persecution. So, what does Descartes say about God?

God is God, so would not deceive him. God as a perfect being cannot be a trickster. Still, there could be an evil genius that is powerful enough to deceive me.

Another relevant film here is The Truman Show: the guy’s life is a reality TV show. He has no idea and believes that this fixed world is reality. Eventually he becomes suspicious. The Truman Show illustrates the idea that what we think is real, is not actually real as well as the idea that there is a deceiver behind the deception. This is also a moment in The Matrix. Either of these films are excellent options to explore in light of Descartes’ Meditation 1 (and Plato’s Allegory of the Cave).

In Meditation II Descartes acknowledges everything that is now questionable, but it then occurs to him that this activity of doubting necessitates that there is an I involved in the cognitive process he is undertaking. At this point he doubts everything until he finds one principle that is absolutely beyond doubt. He concludes, he must exist in some form because he doubts. Here’s his argument: Cogito, ergo, sum (I think, therefore I am).

So, at this point he is certain that he is a thinking thing. This will be his starting point.

Now we must move from this point to prove the beliefs that he began by doubting: the existence of his own body, the existence of the external world, and the existence of God. He must also get rid of this evil deceiver. This process takes up the bulk of the remaining meditations. In the end, he proves God’s existence and determines that the physical world, including his body, very likely exists because God is good and wouldn’t trick us in this way. The problem with his reasoning at this point is that he’s using a fallacious form of reasoning, called begging the question (or arguing in a circle). Descartes uses God to salvage the physical world, yet his proofs for God’s existence depend upon the clear and distinct ideas that were needed to prove that God exists. This is referred to as the Cartesian Circle.

Another important element that Descartes introduces in Meditation II is a wax analogy. He sets up the analogy by describing a piece of wax: It is cold, hard, easily handled, it emits a sound when thumped or dropped, it is sweet to taste, and still smells a bit like flowers. However, if I bring the wax near the fire all of those things change: the taste changes, the smell evaporates, the color is altered as is the texture. “Does the same wax remain after this change?” Descartes says yes.

We cannot understand the wax as the same given our senses. All of those qualities have changed and are no more. So, how do we know that the wax is the same piece of wax as before? How do we know the essence of the wax? Descartes says that it is through an intuition of the mind. The mind has an understanding of the laws and conditions that physical things adhere to or undergo. We can separate these contents out from the sense data and have a more clear and trustworthy understanding of the thing in question.

This is key to rationalist thinking. The rationalist has to rely on nonempirical intuitions, which are grounded in reason.

Here’s a video that highlights some important features of Descartes’ philosophy:


We now turn to discuss the empiricist’s response to the problem of knowledge as we continue our epistemology section.

We start with John Locke, one of the most influential thinkers of the 17th century. Like Aristotle and Newton, Locke believed that knowledge comes from observation and survey of facts about sight, memory, and reasoning. Comparing the mind to a blank slate, Locke believed that the mind is like a receptacle that stores experiences. This is the empiricist tradition.

According to Locke, even though knowledge comes from experience, this does not mean that reason doesn’t play a major role for us. It is from sense experience that we gain simple ideas, which are the foundations of knowledge. Simple ideas can be fused together (by reason) to make more complex ideas. For example, I have the experience of red, sweet, solidity, and my faculty of reason combines these to form a more complex idea like apple.

Locke accepted Descartes’ method of tentative skepticism but questioned Descartes’ move to tie the metaphysical questions regarding God to his epistemological method. From an empiricist’s perspective, God cannot be experienced in the way we typically think of sense experience. Locke also rejected Descartes’ idea that we have “intuitions of the mind.”

Locke emphasized inductive modes of reasoning, which include generalizations. Inductive reasoning is never as secure as deductive reasoning; however, Locke believed that a lot of our knowledge is based on induction—generalizations from various experiences we have had. As such, Locke did not demand “perfect certainty,” which is related to deductive reasoning. Instead, he allowed for varying degrees of probability, which, again, is related to inductive reasoning. Locke did acknowledge there were deductive truths but these come in the form of mathematical reasoning and the validity of deductive inferences.

To unfold these ideas and build our understanding of Locke and his place in the debate regarding the problem of knowledge, we start with Locke’s An Essay Concerning Human Understanding. The overall point of this text is that all knowledge comes from experience. There are no ideas that are prior to experience (a priori).

During Locke’s time, the view that certain ideas are innate was tied to the stability of religion, morality, and political life. Locke explicitly argues against innate ideas, instead arguing that reason is a God-given faculty that we should use to better our lives and our understanding of the world.

As Hewett explains, aside from Locke’s epistemology, his political thought is extremely influential, particularly to the French and American revolutions. He believed humans are capable of organizing society in a rational way. His rejection of innate ideas was intimately linked to this project for it is all too easy to claim all sorts of principles as innate in order to maintain the status quo, meaning that people “might be more easily governed by, and made useful to some sort of men, who has the skill and office to principle and guide them. Nor is it a small power, it gives one man over another, to have the authority to be the dictator of principles, and teacher of unquestionable truths; and to make a man swallow that for an innate principle, which may serve his purpose, who teaches them.”[1] Locke thought humans are autonomous and self-governing because God gave us the faculty of reason.

Hewett continues by explaining that Locke is referring to the content of the mind, not its abilities. Locke clearly believes that we are born with a variety of faculties that enable us to receive and process information (the senses, memory, our ability to use language, etc.) and to manipulate it once we have it, but what we don’t have is innate knowledge or ideas.[2]

Locke must then show how sense experience can reveal the existence of things outside of us. He argues that we must distinguish between the objects of our experience (external objects) and our experiences of those objects (sensations or sense data). Physical objects cause sensations in us and we are directly aware of such sensations.[3]

Locke’s empiricism can be thought of as a representative theory of perception in that humans do not directly perceive physical objects. The physical object causes an idea to arise in our minds and these ideas are representations, or copies, of the physical object. Keep in mind that ideas and qualities are different things. Ideas are “mental entities,” things that exist “in our minds,” whereas qualities are the causal properties (“powers”) of physical objects.

According to Locke, our ideas come in two varieties:

Simple ideas are ideas that cannot be broken down into any component parts. For example, the idea of white. I cannot explain white to you; I can only show examples of white and hope you get it. Simple ideas arise from simple sensations.

Complex ideas are ideas that can be broken down into component parts. For example, the idea of (perception of) a unicorn. I can explain the idea of a unicorn to you. To explain a unicorn all one must do is take the concept of a horse, white, a horn and combine them in a certain way. The idea of an apple (i.e. one’s perception or experience of an apple) might include the simple ideas of red, round, sweet, solid, etc.[4]

From here, Locke makes his famous and important distinction between primary and secondary qualities. For Locke, primary qualities are those properties of an object that are not related to perceivers. The primary qualities are size, shape, motion, number, and solidity. We might say that the object has these properties ‘in and of itself’. Primary qualities, Locke says, are ‘inseparable’ from a physical object, whatever changes it goes through. For example, physical objects always have some shape and size. These properties don’t depend on whether and how the object is perceived by us.[5]

By contrast, secondary qualities are related to perceivers by definition. As we saw, color, by definition, is something that is experienced in vision. So it is a property that an object can have only in relation to its being seen by someone. The other secondary qualities are temperature, smell, taste, and sound. Secondary qualities aren’t possessed by all physical objects, e.g. plain glass doesn’t have a color or a smell. And they aren’t even possessed by the same physical object at different times, e.g. glass is made from sand, and sand does have color. So sand loses its color completely when it is made into glass.[6]

Two ways to tell the Difference Between Primary and Secondary Properties:

  1. To change a primary quality of the object you have actually have to change the object, but to change a secondary property you only need to change the conditions of perception.
  2. Primary properties can be experienced by more than one sense, but secondary properties can be experienced by one sense alone.

Take an apple for example. It is a complex idea composed of, among other simple ideas, the ideas red, round, sweet, and solid.[7]

According to the criteria Locke provides, which of the apple’s perceived properties are primary (really in the apple), and which are secondary (perception dependent, having no reality apart from perception)? Red is secondary- (I would no longer see red if I were to change the lighting or I stared at a bright green poster board. Also I have access to the color of things through only one sense: vision.) Round is primary- (I would have to cut or smash the apple to change its shape. Also, I have both visual and tactile access to the shape.) Sweet is secondary. Solid- primary (sight and touch).[8]

Essentially, we can have knowledge of material objects because some of our sense experiences represent the object’s primary qualities, which are characteristics of the object itself.

Here’s a video that summarizes the empiricist tradition:


In his A Treatise Concerning the Principles of Human Understanding (Principles), Berkeley argues against Locke’s distinction between primary and secondary qualities, and comes to the conclusion that objects are immaterial and are objects of the mind (i.e. ideas). This idea is famously conveyed as: “esse est percipi” to be is to be perceived.


Hume follows the empiricist tradition. In fact he is committed to Locke’s method, but where Locke was generous with doubtful ideas that had no clear experiential basis (the metaphysical ideas of substance and God), Hume was ruthless. In a famous passage he claims that if a principle of knowledge is not grounded in abstract reasoning like math or in experimental reasoning concerning existence, it is mere illusion.

Like Locke, Hume insists that all knowledge begins with experience-basic sensory experience, which he called “impressions.” So, what Locke referred to as “sensations,” Hume calls “impressions.” Hume makes a distinction between impressions and ideas. The difference between the two consist in the degree of mental liveliness and the way they make their way into our thought and consciousness. The strong and lively perceptions are impressions. Hume includes all of our sensations, passions, and emotions as we first experience them. Ideas are the faint images of the impressions in our thinking and reasoning. Hume notes the difference between feeling and thinking. There are degrees of difference between these two. Consider the difference between when you are thrilled with enjoyment versus when you are thinking about how happy you were at that moment. These are two different experiences and the actual feeling is much stronger compared to your remembering the feeling. If you’ve seen the early Christopher Nolan film, Memento, you can see a way in which Hume’s impressions and ideas might work.

Following Locke, Hume makes a distinction between simple and complex ideas. Simple perceptions cannot be broken down, whereas a complex perception can be distinguished by parts. He uses the apple example as well. Let’s consider the color red: I have an idea of red that I can picture in my mind, even when I do not actually have a red object in front of me. I can also have an impression of red when I do in fact experience a red object. The idea and the impression are only different in degree. Again, like Locke, complex ideas are formed from the simple. These do not require an actual experience (e.g. unicorn). Complex ideas are associations of simple ideas.

For Hume, if we want to justify our belief as actual knowledge, we must break down the complex idea into the simple ideas and then find the impression upon which these ideas are based. He is really holding Locke to his word regarding experience being the source of knowledge.

Hume also discusses two types of claims that we make. This is often referred to as Hume’s Fork:

Relations of ideas—math and other claims that are intuitively or demonstratively certain. 3 x 5 is equal to the half of 30. This claim expresses a relation between these numbers. These types of propositions are discoverable by the mere operation of thought and do not depend upon any existent thing in the universe.

Matters of fact—these types of claims are not given by reason. The contrary of every matter of fact is still possible. That the sun will not rise tomorrow is an intelligible proposition and implies no more of a contradiction that the contrary statement, that the sun will rise.

Hume further claims that all reasonings concerning matters of fact seem to be founded on the relation of cause and effect. If we are trying to explain a matter of fact, we give a causal explanation. We can see this from Hume’s example of an absent friend. Where is this person? I believe he is downtown. Why? He told me he had a doctor’s appointment and that his doctor is downton. Alternatively, take the person finding a watch on a deserted island. They would conclude that some person had been there because watches are associated with people. If you hear a voice in the dark, you conclude there is a person there because these are the effects relevant to human beings.

Claims regarding cause and effect don’t come from reasoning, but from our experiences of finding two objects “constantly conjoined.” If we find a new object—an object we have never seen before–we will not be able to find its cause or effects.

We do not discover causation through the properties of the object, either the causes or the effects. The mind can never possibly find the effect in the cause (or in the object itself). The effect is different from the cause. When we hit a cue ball into the 8 ball, the motion in each is different. When the cue ball is moving toward the 8 ball, we can imagine (without contradiction) that the 8 ball will not move, or that it will fly off the table, or that it will move in the opposite way from which we expect. So, why do we give preference to the one idea regarding the 8 ball moving in a single direction? A priori reasoning is not going to tell us why we should prefer one direction or type of movement to another. The effect, which is the way that the 8 ball will move, is based on our repeated experiences. We predict the 8 ball will move in a specific way.

From Hume’s method, it follows that if I am going to make a metaphysical claim about the existence of God, for example, I must be able to identify the idea and impression upon which that claim is based or I must show that it is a relation of ideas. If neither, then the claim must be committed to the flames. Metaphysical claims, by their very nature, cannot be defended by Hume’s method, because these claims are beyond everyday experience. These claims cannot be based on impressions and they are not relations of ideas. Therefore, they cannot be justified.

This poses some serious problems for metaphysics, but also undermines some of the beliefs that are most essential to our everyday reasoning and experiences. Hume singles out three extremely common beliefs for analysis under this method: causation, the principle of induction, and our belief in the external world.

The principle of causation states that every event has a cause (or a set of causes). This is how we explain things. For example, if your car doesn’t start, we search for the cause by looking at the batter, the carburetor, and so forth. We may not find the cause, but we know that there is one. We presuppose that every event has its cause. Neither experience nor reason can provide us with evidence that causal relationships exist. we observe no power or force that enables causes to produce effects. All we observe is one event associated with another and when we see this pairing repeatedly (constantly conjoined), we jump to the conclusion that such events are connected. So, these inferences are based on habit or custom, not logic or empirical evidence. Ultimately, this means that we cannot trace the causal connection back to any impression we’ve experienced. Causation then is simply a matter of expectation based on habit or custom because we find two events or things constantly conjoined.

Because of our belief in causation we are able to think beyond our immediate ideas and predict the future. This depends upon our ability to believe that our observations of the present will have some relevance in the future. This means that we can draw inductive generalizations from our experiences of the present to make a prediction about the future. In the morning when I wake up I expect the sun to rise.

Hume demonstrates this point: our senses inform us of certain properties of bread: color, taste, size, shape. But neither reason nor the senses can ever inform us of those qualities which make that object fit for our nourishment. Even though we cannot know the natural powers and principles, we always assume that when we see like qualities they will have like powers. I expect the effects to be similar. So, when I see a loaf of bread, I expect it to have a certain taste and I expect that it will nourish me. Why? Because other breads have had a certain taste and have nourished me. This is not known by the mind. Instead, I hold this belief because this has happened all of my life. Even though I expect the bread to be similar there is nothing in the object itself that tells me this is the case; this is something I infer. The consequence that I reach is not a necessary one.

Much like the argument, regarding cause and effect, it is only from experience that we know the properties and effects of things and events. However, with this argument he makes a distinction:

1) I have recognized a certain cause and effect relationship in my past experience

2) I predict that a similar cause and effect relationship will hold in the future.

When pressed to explain why such an inference is reasonable, Hume says we cannot do so by reason or by an appeal to experience. Hume argues that we cannot appeal to matters of fact to justify our predictions. So, there is no justification. In sum, he goes on to refute causation and the principle of induction by showing that neither can be defended either as a relation of idea or as a matter of fact.

Overall, I tend to think of Hume as taking Locke’s theory to its logical and skeptical end, although I am not totally sure that’s fair to Locke. Still, Kant famously claimed that Hume awoke him from his “dogmatic slumber.”

Here’s a set of videos that summarize Hume’s epistemological positions:


For a brief overview of Kant’s views on epistemology (as well as metaphysics), please review Dana Andreicut’s “Kan’t and Rand on Rationality and Reality.” The article will cover an overview of his own view as well as notes relating Kant’s work to Rand, Hume, and Descartes.

Also, take a look at the following video, “Beginner’s Guide to Kant’s Metaphysics and Epistemology”:


Check Your Understanding

Directions: Answer the question below and check your answer before moving on. Use the arrow below on the right to move to the next question. When you have answered all four questions, click Finish.


  1. Hewett, C. (n.d.). John Locke's Theory of Knowledge. Retrieved August 10, 2020, from http://www.thegreatdebate.org.uk/LockeEpistem.html
  2. ibid
  3. Vaughn, L. (2014). Living philosophy: A historical introduction to philosophical ideas. New York, NY: Oxford University Press, 240.
  4. John Locke and the Causal Theory of Perception. (n.d.). Retrieved August 10, 2020, from http://faculty.fiu.edu/~harrisk/Notes/Epistemology/Locke's Epistemology.html
  5. ibid
  6. ibid
  7. ibid
  8. ibid


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An Introduction to Western Epistemology Copyright © 2020 by Heather Wilburn, Ph.D. is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.

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