Justified True Belief, or JTB, has it’s roots in Plato’s dialogues and is often used as a working model for knowledge despite some significant shortcomings. The idea consists of three components, making up what is called the tripartite analysis of knowledge:
- Proposition P is true.
- An individual S accepts P - that is, they believe P is true.
- S believes P is true based on a real justification.
The third point - the justification - is the crux of this analysis as it separates knowledge from lucky guesses. Imagine letting a child pick from three colored boxes, one of which has a toy inside. The child may claim that the red box has the toy inside since that is her favorite color, and it might be true, but this cannot be counted as knowledge because the reasoning is illogical. If instead, the child had looked at the sizes of the boxes and decided the red one contained the toy as it was the only one big enough to fit it, and she was right, then one could claim that she knew the toy was in the red box.
This tripartite analysis was widely accepted until 1963 whereupon Edmund Gettier released a short paper outlining several examples in which these three conditions were met but most people would be hesitant to call the result true knowledge. These are now called Gettier cases and tend to center around justifications that are logical, contain a flaw based on unlikely bad luck, and yet turn out to be true anyway, rendering the belief true and justified but for illogical reasons.
One of the original famous Gettier cases involves a man owning a Ford and another being in Barcelona.
Proposed additions to the tripartite theory to address the deficiency include "No false lemmas" (in which the justification cannot be based on a falsehood), Nozick’s ‘sensitivity' clause (which modifies the second statement to make S believe P only if P remains true) and a few other ideas, but none have been universally accepted as a patch yet.