“How Do I Know I Know What I Know?”: A Brief Overview of Theories of Knowledge

“How do you know you know?”: A Simple Guide to Western Theories of Knowledge

How do we know the things we “know” are in fact knowledge? I might say that I know wet hair causes colds, but do I really know this? Is learning this from your grandmother really a reliable source of knowledge? What counts as knowledge has been debated for centuries, and epistemology (philosophy of knowledge) has not yet agreed on a unanimous definition of knowledge. Western epistemology is the –ology study of episteme– knowledge from the tradition of Western philosophy. Since the ancient Greek times, we have come a long way in the realm of epistemology.

There are many theories of knowledge, though none are yet a perfect theory. From shaky beginnings of the Justified-True-Belief account (JTB), it has blossomed into more refined knowledge theories. In this essay, I will explicate several main theories of knowledge: The Traditional Account, Causal Theory, Foundationism, Coherentism, Reliable Indicator, Naturalized Epistemology, and finally Scepticism. I will give a brief outline of these theories one by one in the order indicated above. Let us begin with a look at the traditional account.


The traditional account of knowledge is known as the Justified-True-Belief (JTB) account. The traditional justified-true-belief (JTB account) is credited to Plato which tries to provide conditions for knowledge that must be satisfied if we are to say we have knowledge of x. The JTB account says that anything considered knowledge must be 1) believed, 2) justified, and 3) true. For something to be known, we must first believe it, it must be justified – we must have reasons for our belief, and it must be true.

The conditions in the JTB are explained as follows. First, if something is rejected (non-belief), we do not know it to be the case because we posit it as false. Second, if something is false it is not knowledge because if I did not break my arm, I cannot know that my arm is broken. Lastly, we cannot know things unless there’s sufficient reason to show that our belief relies on truth, since false things cannot be known. Furthermore, we must make our knowledge clear, public, and explicit or knowledge is just a hunch. Knowledge also means it can be known by anyone. Though this seems like a solid and basic account of knowledge, it certainly comes with many flaws.

Knowledge in the Traditional Account is supported like a tripod with 3 legs: Justification, Belief, and Truth. Without each leg, knowledge collapses.

The JTB has many loopholes as demonstrated by Edmund Gettier in his famous 1963 paper, “Is Justified True Belief Knowledge?” Gettier explains cases where the conditions of something being justified, true, and believed still leave us intuitively thinking we do not have knowledge. These have come to be known as “Gettier cases”. To keep this short, I will use my favorite simple case from Roderick Chisholm (1966) as an example about the lamb in a field:

  1. The farmer sees what looks like a lamb in the field.
  2. This leads the farmer to believe that there is a lamb in the field. (justified + belief)
  3. The “lamb” the farmer sees is just a dog that looks like a lamb to the farmer.
  4. There is a real lamb hidden behind a tree in that field. (belief is true)

Here we see that the farmer believes there is a lamb in the field, justified by his perception of a (dog that looks like a) lamb, and his belief “there is a lamb in the field” is true because there is a lamb hidden behind a tree. The farmer does not know there is a lamb, and thinks the dog is a lamb. This leaves much to be desired because we might say “well he doesn’t know there’s a lamb in the field because he never actually saw a lamb.” He has “knowledge” according to the three conditions being fulfilled, but we see he is mistaken in his belief that the dog is a lamb. There are many loopholes in the traditional JTB account and since then many more theories of knowledge have been proposed with the aim of better capturing knowledge when knowledge is due. One of these theories is the Causal Theory.      


The Causal Theory of Knowledge was proposed by Alvin Goldman in his 1967 paper, “A Causal Theory of Knowing.” Goldman details knowledge as something that occurs externally when we are hooked up to the world in the right way. As Goldman says, for subject S and proposition p, “[a] necessary condition of S’s knowing p is that his believing p be connected with p by a causal chain” (361). What he means is that if our inferences about the world links to how the world really is, in a way that our inferences mirror what the actual causal chain from the sequence of events that lead to our belief is, then we have knowledge. For instance, he details one case about a volcano that erupts.

The Causal Theory of Knowledge states that for knowledge, a person must correctly reconstruct or “mirror” the important links in the causal chain from the thing to the inference. Above, the red arrows indicate a causal chain, the blue arrows indicate the inferences, and the solid black line in the middle is the mirror, reflecting the causal chain. Since the reflection is identical, there is knowledge.

If there is a volcano that explodes and leaves hardened lava rock around the base of the volcano, and someone (S) sees the volcano and the lava rock around the base of the volcano, then when S infers P “this volcano has erupted in the past”, it is knowledge. This fulfills a belief that is 1) justified because the fact that the belief is causally connected in an “appropriate” way with S’s believing P, 2) it is true, and 3) S believes P. It is a justified true belief. But consider a similar example that does not lead to knowledge: A person removes the solidified lava and replaces it with different solidified lava. Now, when S infers P in this situation it is not knowledge because the causal chain from the eruption of the volcano to S’s perception of P is broken. In summary, the Causal theory tells us that knowledge is gained from the world when we correctly infer the important links in a causal chain that have occurred in the world. This was a short explanation of the Causal Theory, let us look at the Pyrrhonian Problematic, Foundationism, and Coherentism, some very different theories.


The Pyrrhonian problematic details that when we justify a belief, we must justify it only by justified statements. When I say, “Jane is at the store” you might say “but how do you know justify that is the case?” I can then say, “I saw her at the store”, to which you respond, “how do you know you saw her?” I respond, “because my visual perception indicated her to be there.” There must be always be a justification to any claim. The Pyrrhonian Problematic says that justification (one of the essential requirements to knowledge) is either:

  1. Infinite in regress (a is justified by b, which is justified by c, which is justified by d, …, ad finitum).
  2. Circular (a is justified by b, b is justified by c, and c is justified by a).
  3. Foundational (a is justified by b, b is justified by c, and c does not require justification).


Foundationism stems from answering the Pyrrhonian problematic. Roderick Chisholm is a modern supporter of the foundational theory of knowledge. In his 1964 book Philosophy, he defends the Doctrine of the Given which says that there are beliefs that are “basic” in the sense that they are self-justified. Chisholm’s theory has two main premises:

  1. Every statement is justified at least in part by a basic belief.
  2. These basic beliefs are self-justified.

What he says here is that for knowledge, any statement must be justified by a basic belief, and these basic beliefs do not require justification because they are justified just by being what they are. These basic beliefs are “appearances” or perceptions that intuitively occur to us that we know we are having. For instance, when I look outside and see the sun, I know it is bright from the mere fact that it appears subjectively bright to me. I cannot argue the brightness as it appears to me. This was a very brief overview of Chisholm’s Foundationism, let us move onto another solution to the Pyrrhonian Problematic by looking at Coherentism.

Chisholm says that all knowledge is a superstructure supported by basic beliefs. I depict his theory as a “house”. The basic beliefs C (red) are the supports and the base level of the home. Belief B is inferred from C, making the second level. Belief A is inferred from B, making the top level.


Coherentism attempts to solve the justification problem by following the route that all justification is circular in nature. By implementing a theory of knowledge that employs circularity, it attempts to situate a belief in a strong web of conviction. A proponent of Coherentism was Lawrence Bonjour in his 1976 article “A Coherence Theory of Empirical Knowledge.” The Coherence Theory of Knowledge is in opposition to Foundationist view and it does not posit “basic” beliefs. The theory says that the only way to avoid infinite regress is to move in a circle. Coherence theory situates a belief within a coherent system of beliefs and for proper justification of belief b:

  1. b must be inferable from other beliefs, and have inferable interrelations within a set of beliefs
  2. The set of beliefs to which b belongs must be coherent (clear, logical, consistent, whole)
  3. The set of beliefs to which b belongs must be justified
  4. b’s justification regarding the set of beliefs it belongs to

In short, belief b must have a place within a set or system of beliefs and have many inferences from within this system. We might see this as a type of “belief net” that catches a belief from falling through and crashing if it can be inferred from other beliefs in that net; inferences are the glue that hold beliefs together. For instance, if I want to know if I have knowledge, I must have a solid set of beliefs for which to relate this belief to – like the set of beliefs of mathematics. If I see a problem in math I have never experienced before, and come to an answer, I can know the answer to be true by situating in within my set of beliefs about mathematics. If the question is a multiplication question, I relate my answer to the beliefs of the rules of multiplication and addition.

Bonjour’s Coherentism depicted as a cartoon. Within the mind is a system of beliefs connected to each other as solid knowledge (black lines). A new belief, b, is being situated within the system of beliefs through inferences (depicted by green lines). Supported through inferences, b is now “glued” to the system and becomes part of it. Each belief supports each other circularly and gains strength through the multiple inferences.

If I want to know that 12×12 = 144 I can know this through knowing that 10×10 = 100 so the answer is higher than 100. That is one inference. A second inference is that I know the rules of multiplication, a third is the method I use to arrive at my answer. Did I use a calculator? The calculator is programmed to not present false operations and has a reliability of above 99.999%. If I used pencil and paper, I might trust that the educational system and teacher that taught me would not present me with false information because the societal system does not want to train up mathematically incompetent workers. Sufficiently, I could ask a friend to also check the answer. So, we have the premise 12×12 = 144 and want to know if this is knowledge:

  1. 144 is higher than 100 and 12×12 should be higher than 10×10
  2. I was taught the rules of mathematics from a reliable professor
  3. I checked the answer on a calculator and calculators are highly reliable
  4. I double-checked my answer and arrived at the same one twice
  5. I asked someone to check the answer and they arrived at the same conclusion
  6. I trust in the educational system, it generally provides reliable mathematicians

This is our set or systems of beliefs for which the answer “144” can be inferred from. Once we situate it within this web, the multiple inferences show that this is knowledge because it reliably and logically fits within the system. While Foundationism and Coherentism attempt to solve the Pyrrhonian Problematic by an internal account of knowledge, there are other theories such as the reliable indicator theory of knowledge that take an external approach.


The Tracking (aka. Reliable Indicator) Theory of Knowledge was proposed by Robert Nozick in his book Philosophical Explanations (1981). The Reliable Indicator Theory of Knowledge says that subject S knows a proposition p when:

  1. p is true
  2. S believes p through method M
  3. If p is false, and S uses M to arrive at a belief about p, then S would believe p is false
  4. If p is true, and S uses M to arrive at a belief about p, then S would believe p is true
  5. There is no other M that S can use to arrive at p that would more strongly satisfy conditions 1-4

When one arrives at inference p through M, it must satisfy conditions 3 and 4 in “all possible worlds.” What this means is that if S uses M to arrive at the proposition “my grandmother is at the store” through method of hearing her say so on the phone, then this method must work when she is at the store or not at the store. In the possible world where she decided to lie to S that she was at the store when she was in fact not (e.g. so S would not visit her because she wanted to be alone), the method of hearing her on the phone does not satisfy condition 3 because it’s false that she is at the store, but S believes she is. But if S rather used the method of observation – to go to the store to see if she is there – then S would come to believe “my grandmother is at the store” when she is there and “my grandmother is not at the store” when she is not there. This method M satisfies condition 5 because it is better at satisfying conditions 3 and 4 than the alternative method of hearing her on the phone.

Reliable Indicator The theory is also known as a Reliable Indicator Theory. What this means is that the method that S uses must be reliable in the sense that it will track the truth of proposition p properly in all possible situations. In situations where p is false, M must lead S to believe it is false; in situations where p is true, M must lead S to believe that p is true. Reliable indicators reliably indicate the truth of p. Reliable Indicator Theory shows that we must use method M as an indicator of truth, but there is another Reliable Process Theory that is quite similar.

Possible World 1: Grandmother is at storePossible World 2: Grandmother is at home
Method M1 (Phone call)1. Grandmother doesn’t lie
2. Grandmother lies
1. Grandmother doesn’t lie
2. Grandmother lies
Method M2 (Visual Perception)1. Grandmother doesn’t lie
2. Grandmother lies
1. Grandmother doesn’t lie
2. Grandmother lies
Using method M1 and M2 in two possible worlds (situations). Within each world is two conditions: one where grandmother lies about her whereabouts, and one where she tells the truth. Green conditions show adherence to Reliable indicator conditions 3 and 4 and red conditions show they fail conditions 3+4. Condition 5 is satisfied if S would choose M2, since it more reliably satisfies conditions 3+4.

Reliable process. A reliable process is one in which proves to provide truth a high percentage of the time. For instance, visual perception is deemed as a reliable process because what we see is generally true, especially under favorable conditions. We know that under sufficient lighting, at a good distance, and with enough time for visual analysis, the things we perceive through visual perception are mostly what corresponds to the world. Though we do know of visual illusions, these are edge cases and only occur very rarely. A reliable process we use for knowledge acquisition and justification must give truth a very high percentage of the time, which makes it a process that is reliable. Reliable processes are things that we possess, but naturalized theories posit that these reliable perceptual processes arose through natural selection.


We have looked at knowledge theories through the lens of rationality and purposeful activity to truth, but naturalized epistemology places knowledge in the hands of nature. For instance, Murray Clarke, Professor of Philosophy at Concordia University, in his 2004 book Reconstructing Reason and Representation attempts to place Nozick’s Reliable Process Theory of knowledge within evolutionary theory, saying that reliable processes were selected for through natural selection (78-81). By selecting for reliable processes that are trustworthy, it confers a fitness advantage, by letting us know what we perceive is true or false with high certainty. It does away with false positives and false negatives, so we know when berries are good to eat or are poisonous, through the reliable senses of smell, sight, feel, and taste.

Weak Replacement. Weak replacement theory says that philosophy alone is not the path to knowledge but requires the help of science. Naturalized epistemology also attempts to place philosophical epistemology within a partnership with science. By informing science of what truth is and how it is obtained, science can find the natural and physical basis of our thought process to inform philosophy once again of the details. Philosophy defines and guides, and science takes care of the physical details. For instance, if philosophy says that only reliable processes can give truth, then science can determine which processes are reliable through quantitative experimental methods. Though we have seen several theories of knowledge, I left the best for last – Philosophical Scepticism.    


I decided to end off with one of the earliest theories of knowledge. It was depicted in ancient Greek times in the Hellenistic period, but the modern proponent of Scepticism is Rene Descartes. Descartes in meditations I and II of his Meditations on First Philosophy wants to find sure knowledge by employing a method we now call Radical Scepticism. Radical Scepticism attempts to find out foundations of knowledge that can be certainly known by first rejecting large categories of things we know through sceptical and critical evaluation.

At one part of the writing (meditation II), Descartes comes to conclude that he can know nothing of the external world or anything at all except the fact that he is thinking – cogito ergo sum – this he can know for sure. It is possible he is being fooled by an evil demon who gives him perceptions that appear true, but they are in fact illusions. He also concludes that he can never know that he is awake – he could be dreaming because there is no certain indicator that one is asleep or dreaming. We do sometimes have vivid dreams that seem real, so what he was experiencing in that very moment it seems he is awake may as well be a dream. To know he is awake, he must have a sure indicator that tells him that he’s awake. The problem is that even if he found such an indicator, there’s no way to know he dreamt this up or that the result from the test is just a dream itself. Barry Stroud clearly explains this in his work “The Significance of Philosophical Scepticism” (1984). The idea that we can never truly know if we are being fooled by an evil demon or that we are asleep or awake, and thus know anything from the external world, is, in a nutshell, Philosophical Scepticism.

Descartes’ Argument

  1. If I know that P, then I know that I am not dreaming P.
  2. But, I don’t know that I am not dreaming that P.
  3. Hence, I don’t know that P.


Western Epistemology attempts to focus on knowledge as a personal or physical process either internally as with Bonjour’s Coherentism and Chisholm’s Foundationism, or through external methods like Goldman’s Causal Theory, Nozick’s Tracking Theory, or Clarke’s Naturalized Epistemology. Philosophical Scepticism is another breed of knowledge theory that says that 100% certain knowledge of the external world is impossible, though as an indefeasible theory does come with its shortcomings, it certainly cannot be ignored. To this day, theories of knowledge are expected to answer the sceptic in some form.

In all, I believe that Reliable Process theories are our best bet to understanding knowledge, especially with the aid of science to tell us how precise each process is. By understanding the process at a physical level, and determining a process’ reliability, we can certainly roughly determine a belief’s truth at a moment’s notice if we do not have access to time and quantitative analysis or through quantitative certainty if the truth is important. A rough analysis such as when requiring an immediate or superfluous answer “what is the best food to purchase for dinner?”; or very analytically through quantitative methods if we have time and the knowledge is deemed important “which witness is most reliable in the murder case?”


Works Cited

Bonjour, Laurence. “The Coherence Theory of Empirical Knowledge.” Philosophical Studies: An International Journal for Philosophy in the Analytic Tradition, vol. 30, no. 5, 1976, pp. 281–312.

Chisholm, Roderick. “The Myth of the Given.” Epistemology: An Anthology 2nd ed., edited by Sosa, Ernest et al., Blackwell Publishing, 2008, pp. 80-93.

Clarke, Murray. Reconstructing Reason and Representation. MIT Press, 2004.

Descartes René. Meditations on First Philosophy: With Selections from the Objections and Replies. Edited by John Cottingham, A Latin-English ed., Cambridge University Press, 2013.

Gettier, Edmund L. “Is Justified True Belief Knowledge?” Analysis, vol. 23, no. 6, 1963, pp. 121–123.

Goldman, Alvin I. “A Causal Theory of Knowing.” The Journal of Philosophy, vol. 64, no. 12, 1967, pp. 357–372. doi:10.2307/2024268.

Nozick, Robert. “Knowledge and Skepticism.”  Epistemology: An Anthology 2nd ed., edited by Sosa, Ernest et al., Blackwell Publishing, 2008, pp. 255-279.

Stroud, Barry. “The Problem of the External World.”  Epistemology: An Anthology 2nd ed., edited by Sosa, Ernest et al., Blackwell Publishing, 2008, pp. 7-25.

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