Does Rene Descartes View Knowledge as Justify True Belief?

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To begin, it's probably worth noting that these question fall within the domain of epistemology, or the theory of knowledge. Epistemology tries to answer two basic questions: (1) what does it mean to know something? (2) What do I, or we, as human beings, know?

The JTB theory as a definition of knowledge:

You should understand the JTB theory as an answer to the question: "What does it mean to know something?"

When we talk about knowledge in this context, we're concerned with is called propositional knowledge. For instance, Tom knows that kangaroos hop around on two legs. More generally, propositional knowledge is knowing that P. (A proposition is a sentence that can be either true or false.)

We can immediately specify two conditions that must be fulfilled for someone to know that something is true.

1. BELIEF:

• Believing that p is necessary for knowing it.
• If S (an arbitrary person) knows that p, then S believes that p.
• It seems impossible for someone to know that p, without believing that p. EXAMPLE: Although Sue knows that possums are mammals she does not believe that possums are mammals. This seems self-defeating, and nonsensical.
• Although belief is necessary for knowledge it is not sufficient for knowledge. In other words, just any old belief will know qualify as knowledge. For example if John believes that there are unicorns in the garden, this is clearly not a case of knowledge

2. TRUTH

Truth is also necessary for knowledge. Alternatively, for a belief to count as knowledge it must at least be true. Whenever someone knows that p, p is true. If you know that p, then p is true.

Consider an example:

In fact, Sue is guilty of stealing the car, but the jury knows that she is innocent.

If you said that, it would sound like you were contradicting yourself.

It'd be okay to say: In fact Sue is guilty of stealing the car, but the jury believes that she is innocent. In fact Sue is guilty of stealing the car, but the jury thinks it knows that she is innocent. But it seems for the jury to really know that Sue is innocent, though, it has to be the case that Sue is innocent. You can't know things which are false. You can only seem to know them, or falsely think that you know them.

3. So far we have two conditions for knowledge, truth and belief. But "TRUE BELIEF" is not sufficient for knowledge. They're not enough to guarantee it.

Here're two examples to make this point.

Pete believes that Suzy is having an affair entirely because of his own neurotic fears and without any evidence whatsoever. As it happens Suzy is having an affair, and is doing a near perfect job of concealing it. We would say that Pete does not know that Suzy is having an affair, even though he thinks he knows it.

Or suppose Bill takes medication that has the following side effect: it causes him to be overcome with irrational fears. One of his fears is that he has cancer. This fear is so powerful that he starts believing it. Suppose further that, by sheer coincidence, he does have cancer. So his belief is true. Clearly, though, his belief does not amount to knowledge.

What we have done above is identified two necessary conditions (truth and belief) for knowledge. These are conditions that must be fulfilled if one is to know. The justified true belief theory of knowledge (JTB theory) emerges when one realizes that true belief is not sufficient for knowledge. The two examples above ...