David Weinberger
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Justifying knowledge

31 January 2016

Knowledge is justified true belief. That’s the classic definition from Plato. But what happens if when it comes to making practical decisions, justification is hard, incomplete and unreliable? Maybe that’s the best thing that can happen to knowledge.

Plato, recounting one of Socrates’ dialogues, notes that lots of people have lots of opinions. Plato tells us that there are two distinguishing marks of the opinions that count as knowledge. First, they are true. There’s thus no such thing as false knowledge, only opinions that we were wrong about.

A good guide

But not any true belief counts as knowledge. Socrates expresses this by asking the slave boy Meno (in the dialogue of that name), “If a man knew the way to Larisa, or anywhere else, and went to the place and led others thither, would he not be a right and good guide?”

Yes, of course, says Meno.

“And a person who had a right opinion about the way, but had never been and did not know, might be a good guide also, might he not?” asks Socrates.


“Then true opinion is as good a guide to correct action as knowledge,” says Socrates.

Meno does not fall for the trap, saying that someone who happens to be right about the directions to Larisa might be wrong about other directions. But Socrates counters by saying that so long as the person with an opinion is right, even by accident, there’s no reason to prefer someone who actually knows the directions he’s giving.

Disputing the facts

Now Socrates’ explanation of why knowledge is a better guide to action than right opinion goes off the rails for modern readers: Knowledge is caused by recollection of the essential “forms” we experienced before birth. But even while we reject Socrates’ explanation of the justification of belief, the need for justification remains. That marks a profound shift in how we think about knowledge, and in how we think overall.

Note that the knowledge that Plato and Socrates are talking about, at least in The Meno, is knowledge that leads to right action. Our culture forgot about that to a large degree (pardon my overstatement) as it pursued knowledge as a “pure” product: true justified beliefs about the world for their own sake ... what we today might call abstract knowledge.

I’m in favor of abstract knowledge, but it has had a distorting effect on how we’ve thought about justification. What justifies the true belief that the area of a 3x4 rectangle is 12? The proper application of an immutable law of geometry. What justifies the true belief that there will be a lunar eclipse on March 23, 2016? Universal laws of physics and accurate knowledge of the current positions of the planetary bodies. In both cases, we justify knowledge by deducing it from laws. Deduction is a strong form of justification because it has the force of logic behind it.

But if we’re concerned about knowledge that leads to right action, we often don’t have the luxury of deducing from laws of nature. We’re instead going to have arguments in which we dispute the facts, the trends, the possibilities and the opportunity costs. You’re going to argue for creating a product line extension of our chewing gum called “Adele Chaw” - “Tastes Like a Million Years Ago!”—and I’m going to argue with your market projections and produce my own reasons why it’d be far smarter to do a denture-safe version for the aging Boomer market. The justifications you and I produce are going to be very very different from the justifications for arguments going on simultaneously at, say, the FCC about how to structure a spectrum auction and from the justifications brought forward by teachers arguing over which Mark Twain books to assign.

Righter opinions

As soon as knowledge becomes aimed at right action, not at abstractions, the justifications become more complex, more disputed and themselves become part of the argument. We often will spend most of our time arguing about the justification of our justifications. We will end up less confident that we’re talking about actual knowledge instead of arguing for reasonably right opinions.

But being forced to consider what constitutes justification is not a bad result. It is a good one. It not only leads to righter opinions, it also reminds us how very little we actually know.