Let’s start with a basic definition of a cognitive bias. I’ve broken it down into three parts.
(1) Cognitive biases are features of ordinary human psychology. They’re a product of normal human brain function that we all share.
(2) These are features of human psychology that make us prone to errors in how we form beliefs and make decisions.
(3) These errors are judged to be errors in relation to see accepted standard of “good reasoning”.
The notion of an “error” is a strong one. We wouldn’t call a cognitive bias a “bias” unless it often resulted in judgments that we can all recognize as faulty or irrational in some way.
The whole concept of a cognitive bias is grounded in this idea that there is a gap between how we OUGHT to reason and how our brains ACTUALLY reason.
You should know that among psychologists who work in this area, there is a debate over how to characterize this gap. How are we to best understand what’s going on when human judgment differs from what some normative theory of good reasoning says. Are we systematically irrational creatures? Or is there a way to understand what’s going on which doesn’t entail such a pessimistic conclusion about human reason? Maybe we need to rethink what it means to be rational.
I’m not going to get into this debate here, because it’s a sidetrack that would lead us too far off the path I have laid out for us. But it is an interesting question.
For our purposes I’m going to follow the majority view, which is that our reasoning is prone to error, and that we need to find ways of avoiding these errors or correcting for them.