Justifying Justified True Belief as Knowledge

Laura E Fox
5 min readApr 13


© Taylor Swift, <https://youtu.be/IEPomqor2A8>.

Taylor has a friend named Este. Este confides in Taylor saying that she believes her husband is having an affair. She has observed that her husband has been acting differently, he comes home late with stains of merlot on his mouth and she’s noticed that he’s brought jewellery on their joint account. Este’s husband is having an affair. Because Este has observed a pattern of facts (Justification) that have led her to formulate a belief (Belief) that her husband is having an affair (Truth), she has a justified true belief (JTB). But is Este’s belief the same as knowledge? In this case, the answer is a resounding No, as there must be an element that bridges the gap between belief and knowledge — an element that falls outside the realms of epistemic luck.

Este’s situation is an example of a Gettier problem, where one can hold a JTB that is founded on facts, which by chance happens to be true. Gettier argues that knowledge must not be the result of luck— however, it is important to note that there are two types of epistemic luck: veritic luck which provides that by person’s belief just happens to be true; and reflective luck which informs the person’s justification for their belief. It could be argued that Este’s justification is both reflective and veritic. However, despite the coincidence that her beliefs are true, Este still fails to have knowledge of her husband’s infidelity. In order to convert her belief into knowledge, we must consider an additional element that links Este’s belief irrefutably to knowledge, we can formulate this as JTB + X = Knowledge.

The Safety Condition
One proposed condition for X, is the ‘safety’ condition by Ernest Sosa. The safety condition can be explained as requiring that Este’s belief is formed in a reliable, that is, ‘safe’ manner — that is, had the circumstances been different, Este would not have held the belief that her husband is having an affair. Or to put it another way, Este’s belief is safe in all “nearby possible worlds” — which is defined as all worlds that are sufficiently similar to this one. When combined with JTB, the safety condition can be formulated as:

1. Este believes that her husband is having an affair.

2. Este’s belief that her husband is having an affair is true.

3. Este’s belief that her husband is having an affair is justified in a way that is safe.

When formulated this way, we get a definition that encapsulates the theory that knowledge is true when the justification for that belief is safe.

However, this safety condition still fails to account for the issue of epistemic luck playing a role in a proposition being true. To remove luck from playing a role in knowledge, there is a need to turn the lens of knowledge inwards and consider theories that rely not on external factors, but on the internal mechanisms available through cognitive processing.

The Reliability Theory of Knowledge
Armstrong’s staunch defence of Lehrer and BonJour’s Reliability Theory of Knowledge meets this need by providing that a belief counts as knowledge if, and only if, it is (a) true and (b) formed by a reliable process. A process is considered reliable only if it produces true beliefs in the context of the relevant circumstances. An advantage of the reliability theory is that it avoids the problem of luck by providing that beliefs are formulated through only reliable cognitive processes. For example, I may believe that it is raining outside because I can hear the rain. I go outside and I can see the rain and feel it, therefore on relying on the cognitive processes which are informed by multiple sources of sensory information. That is, I am both perceptually-based and deductively-based in believing that it is raining. However, if we were to apply this theory to Este’s example, she would fail to meet the reliability criteria as her belief is formulated by assumptions made solely on her perceptions and not through deductive reasoning that can support a process of reliable cognitive rationalisation. Ultimately, there are still questions that surround the reliability of Este’s rationalisation which raise more complex issues such as Este’s mental health, attachment style, and the ultimate health of her cognitive processes to rationalise in a highly-emotive situation. These are issues that would be raised in a court, and its one of the many issues that play into the complexities and issues of testimonial evidence in legal settings. However, discussion of this issue falls outside the realms of this essay. The point is made, and in essence:

1. Este’s husband is having an affair;

2. Este believes that her husband is having an affair;

3. Was Este’s belief produced by a reliable cognitive process?

4. No, therefore Este does not have knowledge that her husband is having an affair.

What is notable about the reliability theory of knowledge is that it omits the requirement of justification as a condition for knowledge, and this is due largely to the argument that reliable cognitive processes replace the need for justification. This deconstruction of the JTB is furthered in Zagzebski’s paper ‘The inescapability of Gettier Problems’, where she argues that where any requirement that knowledge be the result of JTB+X, will always result in a lack of knowledge. On this notion, it would appear that knowledge would be better supported by psychological theories of knowledge, rather than Justified True Belief.

It would seem that the theory of JTB+X = Knowledge is no longer sufficient to establish the existence of knowledge, as X appears always to be tied to some form of epistemic luck or lacks the reliability to formulate rationale conclusions to meet the conditions of knowledge. The only path out of this inescapability of Gettier problems is to move towards theories that consider the mental attitudes and cognitive processes that operate as superior foundation for knowledge than Justified True Belief.


Gettier, Edmund. 1963. “Is Justified True Belief Knowledge?” Analysis 23 (6): pp. 121–123

Green, Christopher. 2022. “Epistemology of Testimony.” The University of Mississippi < https://iep.utm.edu/ep-testi/>.

Ichikawa, Jonathan Jenkins, and Steup, Mathias. 2017. “The Analysis of Knowledge.” In Edward Zalta (ed.), The Stanford Encyclopedia of Philosophy.

Orozco, Joshue. 2011. “Epistemic Luck.” Philosophy Compass 6 (1): pp. 11–21

Zagzebski, Linda. 1994. “The Inescapability of Gettier Problems.” The Philosophical Quarterly 44 (174): pp. 65–73



Laura E Fox

LLB (Hons) and BA (Gender Studies and Philosophy) student. A collection of academic essays.