Rationality summary

Let’s start at the beginning: what is rationality? Dictionaries tell us that rational means “having reason.” And reason comes from the Latin word ratio, which means – you guessed it – “reason.”

So, if etymology leads us in circles, could philosophy help? Philosophers state that rationality is the ability to use knowledge to attain goals. Better?

Let’s break that down. The term knowledge refers to justified true beliefs. We wouldn’t credit someone with being rational if they knowingly acted on false beliefs – like looking for a misplaced wallet someplace they knew it couldn’t be. But there’s more to rationality than simply thinking true thoughts like “1 + 1 = 2.” It also helps us do things.

The key message here is: Rationality is a means to an end.

In 1890, the American philosopher William James wrote an essay on the difference between rational beings and nonrational entities.

James observed that if you scatter iron filings on a table and place a magnet near them, they fly toward the magnet and stick to its surface. But cover the magnet with a card and they press against its surface – it never occurs to them to bypass the card and come into direct contact with the object that attracts them. Now consider Shakespeare’s Romeo and Juliet.

Juliet is Romeo’s “magnet.” When there’s no obstacle in his path, he moves toward her in a straight line just as the filings moved toward the real magnet. But here’s the difference. When Romeo finds his path blocked, he alters course. Romeo and Juliet don’t remain on either side of this obstacle, “idiotically pressing their faces against its opposite sides like the magnet and the filings with the card.”

In the play, Romeo and Juliet use their knowledge of the world to overcome hurdles. Romeo scales walls to touch Juliet’s lips, and the couple scheme to deceive their hostile families.

For James, this is what sets nonrational entities and rational beings apart. Iron filings move in a straight line toward their goal. But their path to that goal is fixed – that’s why the card impedes them so easily. It’s the other way round for rational beings. Romeo and Juliet’s desired end – being together – is fixed, but they’re highly flexible about how they achieve that goal.

This is human rationality in action: when one path is blocked, we can always try another.