Is justified true belief knowledge?

Knowledge is a type of belief. For example, if you know that grass is green, then you necessarily believe that grass is green, too.

But knowledge isn’t merely belief. For example, let’s say that I believe that grass is orange. Even though I believe that grass is orange, I don’t know that grass is orange. So, knowledge isn’t merely belief.

Knowledge is true belief. The reason I don’t know that grass is orange is that it’s not true that grass is orange.

But knowledge isn’t merely true belief. For example, let’s say that you flip a coin and that I believe that the coin will land on heads. And let’s say that the coin does happen to land on heads. But obviously I didn’t know that the coin would land on heads. So, I had a true belief, but I didn’t know. So, knowledge isn’t merely true belief. The belief must also be justified somehow.

So, it would seem that justified true belief is knowledge.  But in 1963, Edmund Gettier published a short paper that challenged that conception of knowledge.

In “Is Justified True Belief Knowledge?”, Gettier presented two scenarios in which a person has a justified true belief that we wouldn’t consider knowledge. I’ll describe the first scenario.

Smith goes to a job interview. The boss pulls him aside and tells him that the other man, Jones, is going to get the job. So, Smith now has a justified belief. He justifiedly believes that Jones will get the job.

Now let’s say that Smith knows that Jones has 10 coins in his pocket. It doesn’t matter how he knows. Let’s say that all of the coins in Jones’s pocket fell out of his pocket and Smith counted them as he helped Jones pick them up.

From his justified belief that Jones will get the job and his knowledge that Jones has 10 coins in his pocket, Smith infers that the man who’s going to get the job has 10 coins in his pocket. So, Smith has another justified belief. He justifiedly believes that the man who’s going to get the job has 10 coins in his pocket.

But unbeknownst to Smith, Smith has 10 coins in his pocket, too. And unbeknownst to Smith, Smith is going to get the job. So, the man who’s going to get the job has 10 coins in his pocket. That means that Smith’s belief that the man who’s going to get the job has 10 coins in his pocket is true as well as justified. So, Smith had a justified true belief. But it seems like Smith didn’t know. So, justified true belief doesn’t seem to be knowledge.

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