In this post, I want to look at the notion of rationality and gain an intuitive understanding of what we might mean when we say that something is more or less rational.
Broadly, there are two common senses in with the term is used.
One is in the sense of what’s called epistemic or theoretical rationality. Intuitively, this is the kind of rationality that aims for the truth. The practice of epistemic rationality involves making inferences from the things one believes to the things that are logically entailed by those beliefs.
The second sense of rationality, to be distinguished from epistemic rationality, is practical rationality, which is about deciding upon actions that one could take which cohere with one’s goals. From the perspective of practical rationality, believing something is just another action, and whether or not it’s rational to do so depends on the degree to which one can expect that action to take one closer to one’s goals.
For an example, let’s take Pascal’s Wager. The idea is that we can’t be certain whether God does or does not exist. But we can cultivate a belief one way or the other by selectively exposing ourselves to the right experiences. The epistemic rationalist would say that the thing to do is to collect evidence and reason carefully about it, and believe whatever is most strongly supported by the evidence. Pascal, in a famous example of practical rationality, looks at the cost/benefit analysis. Suppose God does exist. In that case, if I believe, then God will reward me with an eternity of bliss. But if I don’t believe, he will punish me with an eternity of hell. On the other hand, if God really doesn’t exist, then it only matters a little bit whether I believe or disbelieve, because there’s no eternity in heaven or hell to worry about. Given this situation, Pascal thinks, it’s in my best interest to believe in God, regardless of what the evidence says.
These are intuitive notions. To use them in an unambiguous way, we’ll have to analyze them further and try to define, as precisely as we can, the criteria of evaluation that will be used to measure some act for its practical or epistemic rationality.