The tripartite view

AQA Philosophy

The tripartite theory of knowledge

The tripartite definition of propositional knowledge can be derived from Plato’s dialogue Theaetetus. It holds that propositional knowledge is true justified belief:

s knows p iff (if and only if):

  1. p is true
  2. s believes p
  3. s has justification for believing p

This definition of knowledge claims that these three criteria (truth, belief and justification) together are equivalent to knowledge. If and only if (iff) refers to the criteria/conditions being necessary and sufficient.

They are individually necessary, meaning that each one is essential for knowledge. In any particular case, if we lack any one of those criteria, we could not have knowledge.

They are jointly sufficient, meaning that if you have all three, you have knowledge, nothing more is needed.


Truth is thought to be a necessary condition of knowledge. Zagzebski, in her article, ‘What is knowledge’, claims that knowledge is a particular type of mental contact with reality. Since reality is ‘everything that is the case’ (to use Wittgenstein’s phrase) i.e. what is true, and knowledge is supposed to be of reality, that provides reason for the criterion of truth.


Belief is thought to be a necessary condition of knowledge. The idea of the mind connecting with reality also provides reason for the criterion of belief since if your mind does not make contact with reality then it seems difficult to see in what sense your mental content might be connected to reality.


Justification is thought to be a necessary condition of knowledge. Justification is the reason or warrant for a belief. Reasons, and so justifications, can be good or bad. Seeing something with your eyes is a good reason, and so justification, for belief in it. Seeing something within a dream is not. There are a variety of types of bad justification such as irrationality, mistakes, logical errors & ignorance.

Zagzebski claims that we think knowledge is good, namely desirable. Having knowledge is difficult as it requires an apparatus of mental abilities but because knowledge is valuable to us, that makes the knower worthy of praise and esteem. It is possible to have a true belief which was not justified if it was gained due to luck/chance, e.g. horoscopes, reading tea leaves or palm reading. True belief can also be gained by irrationality, such as being convinced that someone is a librarian due to seeing them read a book. If they turned out to in fact be a librarian, that would be true belief but not justified because not all book readers are librarians. Luck and irrationality will occasionally produce a true belief, but philosophers would rather explain such events with the phrase ‘a broken clock is right twice a day’, rather than confer the praise and esteem of ‘knower’ to the believer in such cases. This provides reason for regarding justification as a criterion for knowledge.

The issue that the conditions are not individually necessary

Integration: A case where we have knowledge without one of those three criteria would be a counter-example to the tripartite view as it would show that the conditions are not individually necessary. This would mean that s would not know p iff s has justification, truth and belief for p, making the tripartite view of knowledge false.

Critiquing the individual necessity of truth:

Scientific knowledge is what we currently have most reason to believe based on the available evidence at the time. This means that it changes over time. E.g. In the early 1900’s Physicists believed the universe was static and eternal, whereas today most believe it is expanding and began at a point in time at the big bang. This is because more evidence has been gained. Perhaps yet more will be gained to change the current view of the origin of the universe. Scientific knowledge might therefore be false and so seems to be a case of knowledge without truth.

Scientific knowledge would be merely justified belief, where the justification is the scientific method.

If knowledge could be false, then arguably it cannot be knowledge. It seems self-contradictory to say we know something to be true, yet it could be false.

Science can make planes fly. It clearly works. There are some false assumptions because some planes crash, however there must be some knowledge.

Critiquing the individual necessity of belief:

A student learns an answer to a question and then forgets it. In an exam, the question comes up and the answer surfaces in their consciousness, seemingly from nowhere to them, though it happened to have triggered their memory without their realising it. They decide to write it down as they have no better idea, though as they thought that answer popped into their mind from nowhere, they do not believe it is right. Arguably this is knowledge without belief.

Having your memory associate an answer with a question is arguably not the same as truly knowing something. In order to know something, arguably you have to know that you know it.

Critiquing the individual necessity of justification:

Knowledge of our immediate perceptual awareness. E.g if I am looking at a red thing. To claim there really exists a red thing in an external world would require some justification, however merely to know that I am having an experience of redness arguably requires no justification since it is known immediately with no process of reasoning or inference.

If it is possible to doubt my existence (criticisms of the cogito) then that would cast doubt on the claim to know my immediate perceptual awareness.

The issue that the conditions are not sufficient: Gettier cases

Integration: Gettier cases attempt to show that we could have all three criteria, a justified true belief, because of epistemic luck. We wouldn’t want to call that knowledge because then that knowledge would be dependent on luck. In that case, a claim of the tripartite view, that J T and B are jointly sufficient, is incorrect. This would mean that s would not know p iff s has justification, truth and belief for p, making the tripartite view of knowledge false.

Original Gettier case 1: Smith and Jones are waiting for a job interview. Smith gains a justified belief that Jones will get the job, perhaps because the president of the company assures him of that. Smith then sees that Jones has 10 coins in his pocket and so formulates the proposition “the person who will get the job has 10 coins in his pocket”. However, it then turns out that Smith gets the job and that smith happened to have 10 coins in his pocket. The proposition Smith formulated was true, he believed it and had justification for it. It seems he therefore had justified true belief and yet he only arrived at it due to the epistemic luck of happening to have 10 coins in his pocket. This means it is possible to have justified true belief and yet we wouldn’t want to say it was knowledge, therefore the joint sufficiency of the tripartite definition is undermined.

Original Gettier case 2: Smith has the justified belief ‘Jones owns a Ford (car)’ from which he justifiably, through disjunction introduction, concludes that “Jones owns a Ford, or Brown is in Barcelona.”

A disjunctive proposition in philosophy involves the logical operator “or”.

“F or B” is a disjunctive proposition. The whole proposition is true if either A or B is true, or if both are true. It is only false if both A and B are false.

In the Gettier case, Smith has justification for believing F is true (that Jones owns a Ford). If we have a justified belief in a proposition like F, we can connect it through the “or” operator to any random thing we could imagine while still being justified in believing the whole proposition. This is because the whole proposition is true even if only F is true. “F or B” is true even if only F is true. So even if we only have a justified belief in F, we still have a justified belief in “F or B”.

So, Smith thinks “Jones owns a Ford, or Brown is in Barcelona.” If, in fact, Jones does not own a Ford but due to luck Brown really is in Barcelona, then Smith had true justified belief. The whole proposition (“F or B”) is true, because B is true. However, we wouldn’t want to say it’s knowledge, because it was only true by luck. It was luck that Brown was in Barcelona. So again, the joint sufficiency of the tripartite definition is undermined.


Infallibilism strengthens the justification criterion of the tripartite definition of knowledge to indubitable justification. Not any sort of justification will do. There must be no possibility of failure of the support it provides to the truth of the belief. The result is that knowledge must be certain.

Smith’s justification for his belief was not infallible because the president could have been wrong, lying, or a hallucination.

no false lemmas

The no false lemmas theory proposes adding a fourth criterion to the tripartite view. A false lemma is a false belief or step in reasoning.

This view of knowledge is that s knows p if and only if:

P is true
S believes p
S has justification for p
S has not inferred their belief in p from any false lemmas

This can solve Gettier problems because it requires that we analyse the process involved in coming to believe a proposition. It allows us to make sure there are no false beliefs or invalid steps in reasoning involved.

Smith’s belief that the person who will get the job has 10 coins in his pocket was inferred from his belief that jones will get the job. That was a false belief and therefore a false lemma.

Integration: Gettier cases work by showing that we can have the (jointly sufficient) conditions required for knowledge yet not have knowledge. The no false lemmas view can coherently claim that Smith did not have knowledge due to not satisfying the no false lemmas criterion, which seems to solve Gettier problems.

However, the no false lemmas theory assumes that all cases of epistemic luck leading to a justified true belief involve false lemmas. Zagzebski creates a Gettier case which she claims involves epistemic luck but no false lemmas.

Dr Jones has very good inductive evidence (symptoms and lab test) that their patient Smith has virus X. This provides justification on the basis of which Dr Jones forms the belief ‘Smith has virus X’. However, Smith’s symptoms and the lab results are due to an unknown virus Y. But, due to luck, after the lab tests were taken but before Dr Jones formed her justified belief, Smith caught virus X. This means that Dr Jones’ justified belief is true.

 So while the evidence upon which Dr. Jones bases her diagnosis does make it highly probable that Smith has X, the fact that Smith has X has nothing to do with that evidence. In this case Dr. Jones’s belief that Smith has virus X is true, justified, and undefeated, but it is not knowledge.” – Zagzebski

By ‘undefeated’, Zagzebski is indicating that Dr Jones did not infer their justified true belief from a false belief. So the no false lemmas condition has been satisfied. Dr Jones has a justified true belief with no false lemmas. Yet, only because of luck. So, the no false lemmas condition cannot say that Dr Jones does not have knowledge.

Integration: this shows that JTBN are not jointly sufficient for knowledge and therefore cannot be the correct criteria for knowledge.


Virtue epistemology

Sosa’s Virtue epistemology replaces the justification criterion with ‘virtuously formed’.  This involves intellectual ‘traits/virtues’ such as intellectual courage, attention to detail and desire for truth as virtuous in that they enable us to achieve knowledge.

S knows p iff

P is true
S believes p
S believes p because of the exercise of intellectual virtue

You have knowledge if you have truth, belief and the belief resulted from intellectual virtues.

Sosa creates an analogy to explain his theory of an archer shooting an arrow at a target.

Accuracy. An arrow accurately hitting a target is analogous to a true belief. This is not enough to be knowledge because accuracy can result from luck, as Gettier shows.

Adroitness. An arrow shot adroitly (skilfully) is analogous to having intellectual virtues. However, even if the arrow was shot well and was accurate – even if someone has intellectual virtues and a true belief, that still does not rule out luck. For example, the arrow could even be shot well, be blown off course, and then blown back onto course.

Aptness. An arrow accurately hitting a target because it was shot well (adroitly) is analogous to having a true belief because of intellectual virtue. This is called aptness. There must be a causal relationship between accuracy and adroitness to truly rule out the possibility of luck. If a person has a true belief because of their intellectual virtue, then they do not have it because of luck.

Barn county as a response to virtue epistemology. Henry is driving through Barn County, a countryside where there is one real barn and many fake barns that look real when viewed from the road. Whenever viewing a barn Henry thinks “there’s a barn”. Most of the time his beliefs are false but in the one case of the real barn his belief is true.

The problem is that in barn county this belief would be false most of the time. It was only luck that it was true in that one instance.

In the barn county scenario, Henry gains a true belief because of intellectual virtue. However, it was only luck that the exercise of intellectual virtue caused a true belief in that situation.