Epistemic Justification: What is Rational Belief?

Author: Todd R. Long
Category: Epistemology
Word Count: 999

Rose, Josh, and Ann are guests at my party. Each believes there’s almond milk in my refrigerator. Rose believes this because she really wants some almond milk and it makes her happy to suppose she’ll get some soon. Josh is merely guessing: the thought just popped into his mind. Ann has just looked in my fridge, pulled out what she recognizes as almond milk and placed it back in the fridge.

Only Ann knows there’s almond milk in my fridge. All three guests have the true belief that there is almond milk in my fridge, but Ann has something the others lack: epistemic justification; her belief is epistemically justified.[1]

This essay introduces the concept of epistemic justification.

A woman looking in a refrigerator. Is she epistemically justified in believing there is almond milk in the fridge?
A woman looking in a refrigerator. Is she epistemically justified in believing there is almond milk in the fridge?

1. Socrates’s Legacy

Although “epistemic justification” is a philosopher’s term, it’s a version of what people have in mind when they say things like, “It’s reasonable to believe what good science indicates,” “Believing in fairies is irrational,” and “The evidence supports the existence of dark matter.”

People generally want to have knowledge. And epistemic justification is widely thought to be necessary for knowledge, which is traditionally understood as involving true beliefs that are epistemically justified.[2]

Long ago, Socrates said that knowledge is true belief plus an account of the reason why.[3] Epistemic justification is whatever can provide that “reason why,” or what makes beliefs rational in a way that might contribute to their being knowledge.[4]

2. Types of Justification

To better understand epistemic justification, let’s reflect on our initial examples.

In our story above, Josh was merely guessing; so he had no reason to believe there’s almond milk in the fridge: his belief was not epistemically justified.[5]

Rose did have a reason to believe: it made her happy. While this wishful thinking gave her a practical or prudential reason to believe there’s almond milk, it did not make her belief even likely to be true: her reason didn’t provide epistemic justification.[6]

Ann also had a reason: she saw what she recognized as a carton of almond milk, held it in her hand, and put it back in the fridge. Given her many past experiences with almond milk, this evidence from her senses gave her a good reason to think it was actually true that there was almond milk in my fridge. And if it was indeed almond milk then we would likely say she knew there was almond milk there.

This explains why Ann, but not the others, had epistemic justification for her belief: she had the type of reason to believe a claim such that, if that claim were true (and it was), she might know that claim.

3. Understanding Epistemic Justification

Epistemologists—philosophers who study knowledge and related concepts–seek a deeper explanation, or a theory, of epistemic justification: what is it?

Evidentialism, the traditional position, says that justification depends on your evidence: experiences that give you good reason to believe a claim.[7] Other theories say that justified beliefs are formed by reliable belief-forming mechanisms (such as perception, which is normally likely to give us true beliefs), or by virtuous belief-formation (such as beliefs formed with intellectual honesty or care), or by properly functioning (the way evolution, or God, intended) cognition.[8]

Despite their differences, most epistemologists agree that epistemic justification provides people with a good reason to believe something is true and makes their beliefs, in some sense, likely to be true.[9] 

3.1. Justification’s Sources

As our examples show, our beliefs have various sources. The standard list includes sense perception, memory, testimony,[10] reasoning, introspection (attending to one’s own mental states), and rational insight (mentally “seeing” the truth such as in “all triangles have three sides”).[11]

This list does not include wishful thinking, tea-leaf reading, or astrology. This is because these don’t tend to get us to the truth, whereas those on the standard list do.[12]

3.2. Justification’s Relativity

Epistemic justification can vary, both from person to person and for the same person, over time. If you’ve studied contemporary physics but I haven’t, then you can be epistemically justified in believing something about quarks, whereas I am not. When people have new experiences or learn new things, they can gain epistemic justification for beliefs that earlier were not justified for them.[13]

3.3. Fallible Justification

The standard sources of justification don’t always get us onto the truth: e.g., long ago, people were epistemically justified in believing that Earth didn’t move. So the evidence we get from the standard sources can be misleading or incomplete. Nevertheless, evidence is an indication of truth to a person. So, when your evidence indicates a claim’s truth to you, you have some epistemic justification for believing it.

According to fallibilism, a belief can be justified even when, unbeknown to us, it’s false.[14] Although we might prefer sources that unfailingly get us onto the truth, most epistemologists accept fallibilism.[15] Indeed if our commonsense view of knowledge is correct, then fallibilism is true. For if having knowledge required that our sources unfailingly get us onto the truth, then we would know very little. Infallibilism about epistemic justification would imply a wide-sweeping skepticism: we could never know that there is almond milk in the fridge or almost anything else![16]

4. Achieving Knowledge-Level Justification

Epistemic justification comes in degrees: one can have more or less of it. When I tell Ann there’s almond milk in the fridge, my testimony gives her more justification for believing there’s almond milk than before my testimony.[17]

What degree of epistemic justification is required for knowledge? Most epistemologists think the knowledge-level standard is high, but not so high that we rarely have knowledge. After all, “knowledge” and “knows” are words we ordinarily use, and we think we often know things like “that’s a dog” (via sensory experience), “2 + 3 = 5” (via reasoning), or “I had blueberries for breakfast” (via vivid memory experience).

5. Conclusion

Most people care, not only about whether their beliefs make them happy, but about whether they’re likely to be true and whether they’re supported by strong evidence. For that reason, we care about epistemic justification.


[1] The term “epistemic” means “pertaining to knowledge.”

[2] However, since Edmund Gettier’s (1963) “Is Justified True Belief Knowledge?”, most epistemologists now think that epistemically justified true belief is necessary, but not sufficient, for knowledge. See The Gettier Problem & the Definition of Knowledge by Andrew Chapman.

[3] Socrates (470-399 BCE), the famous teacher of Plato, says this in section 98a of Plato’s (1980) Meno.

[4] “Rational” means “of or based on reasoning or reason” (The Oxford English Dictionary, 1996, p. 1198).

[5] Some philosophers have argued that it is sometimes, if not always, morally wrong to hold epistemically unjustified beliefs. See Is it Wrong to Believe Without Sufficient Evidence? W.K. Clifford’s “The Ethics of Belief” by Spencer Case.

[6] For some topics, we can be practically or prudentially justified in holding a belief that may, or may not, be epistemically justified for us. For an overview of an argument in favor of believing there is a God that appeals to claims about practical or prudential reasons to believe in God, see Pascal’s Wager: A Pragmatic Argument for Belief in God by Liz Jackson.

[7] For a discussion of one version of evidentialism, see Is it Wrong to Believe Without Sufficient Evidence? W.K. Clifford’s “The Ethics of Belief” by Spencer Case.

[8] For an introduction to some evidentialist and non-evidentialist theories of epistemic justification, see Long (2021). Another option is to say that epistemic justification cannot be analyzed without first understanding knowledge; see Silva (n.d.).

[9] For more on widely shared assumptions, see Long (2021) and chapters 1-2 in Feldman (2003). To better understand what it can be for something to be “likely to be true” see Interpretations of Probability by Thomas Metcalf.

[10] Epistemologists debate whether testimony—beliefs gained from what other people claim, as opposed to first-hand experience—is as fundamental a source of epistemic justification as the others on the standard list. To appreciate the basic debate about this issue, see Take My Word for It: On Testimony by Spencer Case.

[11] For more on sources of justification, see Steup & Neta (2022, sect. 5).

[12] This does not imply that every belief with one of the standard sources is epistemically justified. For example, a quick glance (which is an instance of sense perception) would be insufficient to epistemically justify my belief that there are twenty cows in a field (whereas a quick glance might be sufficient to justify my belief that there’s something brown out there). This example shows why epistemologists look for deeper explanations of why and when the standard sources provide epistemic justification.

[13] These points corroborate the core notion of a central tenet of some feminist epistemologies: everyone has an epistemic standpoint, and thus all knowledge is situated knowledge. See Poole (2021).

[14] Typical non-evidentialists also accept fallibilism. Accordingly, knowledge-level justification requires a belief-forming source that is highly (but not 100%) reliable. Note that fallibilism does not imply that one can know something to be true when it’s false, for truth is also a requirement for knowledge.

[15] A famous exception was René Descartes (2001 [1641]), who thought that knowledge required the impossibility of error. See Descartes’ Meditations by Marc Bobro. A few current epistemologists also accept infallibilism. See Descartes’ “I think, therefore I am”: Descartes on the Foundations of Knowledge by Charles Miceli.

[16] Take our sensory beliefs, for example. Our evidence from sense perception does not unfailingly get us onto the truth; therefore, we’re not infallible in our sensory beliefs. Furthermore, a vivid dream or hallucination can mimic sense perception; thus, the evidence we get from sense perception does not guarantee the truth of what it indicates. To see why some philosophers have taken these facts to support skepticism, see External World Skepticism by Andrew Chapman.

[17] This example assumes a typical instance of testimony in which the person receiving the testimony has reason to think the testifier is trustworthy about the relevant matter.


Descartes, R, (2001). Meditations on first philosophy (J. Veitch, Trans.). trans. John Veitch, The Classical Library. (1641)

Feldman, R. (2003). Epistemology. Prentice-Hall.

Gettier, E. (1963). Is justified true belief knowledge? Analysis, 26(3), 121–123.

Long, T. R. (2021). Epistemic justification. In B. Barnett (ed.), Introduction to philosophy: Epistemology. Rebus.

The Oxford English Dictionary. (1996). The Oxford English reference dictionary (2nd edition). Oxford University Press.

Plato. (1980). Meno (G. M. A. Grube, Trans.) (2nd edition). Hackett.

Poole, M. C. (2021). Feminist epistemologies. In B. Barnett (ed.), Introduction to philosophy: epistemology. Rebus.

Silva, P. (n.d.). Knowledge-first theories of justification. In J. Fieser & B. Dowden (eds.), The Internet encyclopedia of philosophy.

Steup, M. & Neta, R. (2022). Epistemology. In E. N. Zalta (ed.), The Stanford encyclopedia of philosophy (Winter 2022 ed.). 

Related Essays

Epistemology, or Theory of Knowledge by Thomas Metcalf

The Gettier Problem & the Definition of Knowledge by Andrew Chapman

Is it Wrong to Believe Without Sufficient Evidence? W.K. Clifford’s “The Ethics of Belief” by Spencer Case

Take My Word for It: On Testimony by Spencer Case

External World Skepticism by Andrew Chapman

Critical Thinking: What is it to be a Critical Thinker? by Carolina Flores

Interpretations of Probability by Thomas Metcalf

Pascal’s Wager: A Pragmatic Argument for Belief in God by Liz Jackson

Descartes’ Meditations by Marc Bobro

Descartes’ “I think, therefore I am”: Descartes on the Foundations of Knowledge by Charles Miceli

About the Author

Todd R. Long is Professor in the Philosophy Department at California Polytechnic State University where he specializes in epistemology, moral responsibility, and philosophy of religion. He is also an actor (stage & screen), director, screenwriter, rock & roll musician, and public speaker. ToddLong.net

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