This entry in the Oxford University Press series of “very short introductions” was recommended on a popular philosophy blog, so I gave it a try. It deals with questions like these:

What is knowledge? What is the difference between just thinking that something is true and actually knowing that it is? How are we able to know anything at all?

This isn’t a general introduction to epistemology, but since that branch of philosophy is also known as “the theory of knowledge”, it comes pretty close. The author doesn’t provide her own answers to the questions above. Instead, she explains the answers given by various philosophers from ancient times to the present. There are chapters on skepticism and the debate between rationalists and empiricists, but the more interesting discussion begins with what’s known as the “Gettier problem”.

Most philosophers have accepted the idea that a belief counts as knowledge if it is both true and justified. Truth isn’t enough. I might believe there are precisely 11 coins in your pocket, and you might actually have 11 coins in your pocket, but unless I have a good reason for believing there are 11, and not some other amount, I don’t really know you have 11. I’m just making a lucky guess. For me to know you have 11 coins, I need a reason for thinking that’s how many there are, e.g. I saw you empty your pocket and then put exactly 11 coins back in.

A philosopher named Edmund Gettier wrote a short paper in 1963 that challenged the standard idea that knowledge is the same as true, justified belief. He argued that a belief can be very well-justified and also quite true, but not count as knowledge. For example, I might believe you own a Chevrolet, since you bought my Chevrolet a while back. Then, this morning, I noticed that you drove that same Chevrolet to work. So it’s reasonable for me to believe you own a Chevrolet. Most people would say I know you own one.

But what if you secretly sold your Chevrolet to someone else yesterday, and the buyer said you could borrow it for the day. Furthermore, what if you used the money you got from selling your old Chevrolet yesterday to buy a new one last night? You do, in fact, own a Chevrolet, and I have very good reasons to believe you do, but the Chevrolet you own isn’t the one I saw you drive into the parking lot. Do I actually know you still own a Chevrolet or am I merely making a well-founded but lucky guess? My belief that you own a Chevrolet is true, and justified, but, according to Gettier (and many other philosophers), I don’t actually know you own one. For all I know, you could have sold your Chevrolet and bought a Ford last night, and I’d still be convinced you owned a Chevrolet. It just so happens you bought another Chevrolet, which makes my belief that you own one true, but I’m ignorant of the true situation. I don’t know you still own a Chevrolet. I merely assume you do. And my very reasonable assumption just happens to be true.

Philosophers have been analyzing Gettier’s article and offering ways around it for years, but there is still no general agreement as to what knowledge is. Nor is there general agreement about the other questions Prof. Nagel asks. Personally, I think it’s almost impossible to find simple answers to traditional philosophical questions. That’s why the questions have lingered so long. One reason is that philosophers too often try to find “the answer”, arguing that something like knowledge amounts to X or Y, when the best answer is that X, Y and Z, as well as A, B and C, all capture aspects of the problem they’re working on.

So, I recommend Knowledge: A Very Short Introduction, especially if you find topics like the Gettier problem interesting. It’s a good summary of some key issues in the theory of knowledge, although you’ll probably be left with more questions than answers.