What is Knowledge?

Theaetetus: Socrates, I have heard it said by someone that knowledge can be defined as having a belief which is true, along with a justification (logos).
Socrates: A good suggestion.
- Plato, Theaetetus

What is the proper definition of knowledge?

Historians of philosophy differ as to whether Plato settled on a definition of knowledge. It is clear that, for him, knowledge is not sense perception. The visible world is so changing and uncertain that true knowledge about it is impossible. Only the realm of ideas is really knowable. and in his Theaetetus Plato comes very close to concluding that knowledge is justified true belief.

If I know something, then certainly it is something I believe. If I don't believe it's raining, say, then how can I know it's raining? How can I know I've had too much to drink if I don't even believe it? So what I know, I must believe. And what I know must be true. I cannot know something false. I cannot know that Vanna White wrote Gone With the Wind, for example, or that Princess Diana is Chinese. So what I know must be true.

So knowledge is true belief. But are there any true beliefs which are not knowledge? Can I believe something that's true but still not really know it? Suppose that I believe that there are exactly seven stars in the Big Dipper. And suppose I'm right. But suppose that my reason for believing it is that I just pictured the Big Dipper in my mind and counted the stars. Do I know it? No, not till I look at it or look it up. Or suppose I believe you are 22 years old, and suppose I happen to be right. Do I therefore know-your age is 22? No. I just guessed.

So knowledge is more than true belief. Really knowing something means that I have good reasons for believing it. So it seems we can now define knowledge as justified, true, belief. In order that I really know something, then:
       l) it must be true;
       2) I must believe it's true; and
       3) I must have good reasons for believing it.

Can you imagine a situation in which all these conditions are met and we still wouldn't say I had knowledge? Suppose I believe Lisa owns a Mustang. I know she has always owned one, and I saw her drive up in one this morning. Then Darren says to me, "Lisa's got a new Honda." I reply: "Either she owns a Mustang or my name isn't Stanley." That's how certain I am. But suppose that, unknown to me, Lisa has indeed traded for a Honda and has driven her Mustang today while the new car is being serviced. And suppose further that I was mixed up with another baby at the hospital where I was born and so my real name is Ralph Baker. So what I believe is true ... that is, it's true that "Either Lisa owns a Mustang or my name isn't Stanley"- because my name isn't Stanley. and I believe it, and I have good reasons for believing it. But of course we wouldn't say I knew it, for my "good reasons"-have nothing to do with what I believe is true.

Bibliography

Plato, The Collected Dialogues, Princeton University Press, Princeton, 1961. See the Theaetetus.