Inductive And Deductive

There are two ways to build knowledge, and most of us have only been taught one of them properly.

Deductive reasoning works from the top down. You start with a general principle, you apply it to a specific situation, and you draw a conclusion. All humans need sleep. This creature is a human. This creature needs sleep. If the opening principles are right and the logic is clean, the conclusion is as certain as anything ever gets. This is how maths works, mostly, and how a lot of formal argument works, and it has an appealing crispness to it. It is the kind of reasoning we tend to respect, because it feels rigorous, and in the right setting it is. The catch is that it cannot tell you anything that was not already implied by the starting principles. It extends. It does not discover.

Inductive reasoning works from the bottom up. You look at many specific cases, you notice a pattern across them, and you form a tentative general claim. I have now seen a thousand swans and every one was white, so maybe all swans are white. This kind of reasoning is how most science actually happens, and how most of human learning happens, and it is what your brain is doing every time you notice that a certain tone of voice predicts a certain kind of day. It is how we discover things. It is also never final, because the thousand and first case might contradict the pattern. A lot of disagreements between people come down to whether the topic at hand is better suited to one mode or the other, and whether the person arguing is using the right one. When you changed your mind about something big recently, which direction did the change actually come from?

Last week we walked the circle of interpretation. This week we look at the two ways knowledge gets built and at why most of us were only ever properly taught one of them.