Justified True Belief (JTB)

The traditional definition of propositional knowledge is derived from Plato's Socratic dialogue ‘Meno’ and ‘Theaetetus’ where Socrates proposes that knowledge has three essential components – “Justified True Belief” (JBT). Many people have an intuition that the statement “Knowledge is more valuable than mere true belief” is true. The relationship between belief and knowledge is that a belief is knowledge if the belief is true and if the believer has a justification (reasonable evidence) for believing it is true.

It is important to note that JTB isn’t an “official” definition of knowledge, it’s a rough description of a general conception of how certain types of propositional knowledge might arise.

Belief  
Mainstream psychology and related disciplines have traditionally treated belief as if it were the simplest form of mental representation and therefore one of the building blocks of conscious thought.

The concept of belief presumes a subject (the believer) and an object of belief (the proposition).  Knowledge is a mental state.  Knowledge exists in one’s mind, and unthinking things cannot know anything.  Knowledge is a kind of belief. If one has no beliefs about a particular matter, one cannot have knowledge about it.

Truth
Knowledge requires factual belief.  If there are no facts of the matter, then there’s nothing to know (or to fail to know). This assumption is not universally accepted, particularly by proponents of relativism.  The epistemology of factual truth is also hotly debatable amongst the empirical-rationalistic camp.

If a belief is not true, it cannot constitute knowledge. Accordingly, if there is no such thing as truth, then there can be no knowledge.

Justification
Not all true beliefs constitute knowledge; only true beliefs arrived at in the right way constitute knowledge (not just based on luck).  Unfortunately, there is much disagreement regarding how to spell out the details.

The requirement that knowledge involve justification does not necessarily mean that knowledge requires absolute certainty, however. Humans are fallible beings, and fallibilism is the view that it is possible to have knowledge even when one’s true belief might have turned out to be false.

Gettier Case – The Broken Clock

There is a classic challenge on justified belief. Suppose that the clock on campus (which keeps accurate time and is well maintained) stopped working at 2:30am last night and has yet to be repaired. At exactly twelve hours later, you lock at the clock and form the belief that the time is 2:30pm. Your belief is true since the time is 2:30. And your belief is justified, as you have no reason to doubt that the clock is working, and you cannot be blamed for basing beliefs about the time on what the clock says. Nonetheless, it seems evident that you do not know that the time is 2:30. If you had walked past the clock a bit earlier or a bit later, you would have ended up with a false belief rather than a true one. This is an example of an ‘academic’ Gettier case in which one can have JBT but not knowledge.