Peirce was a logician, mathematician, physicist, and among many other things, a founding mind of American pragmatism. But his real obsession was how we form beliefs… and what it takes to change them.
He believed that truth wasn’t something handed down. It was something you worked toward. And the way you got there wasn’t by doubling down… it was by being willing to be wrong.
For Peirce, doubt wasn’t a weakness. It was the start of real thought.
He outlined three basic ways humans reason:
- Abduction: What might be true, based on an informed guess.
- Deduction: What must be true, if certain rules hold.
- Induction: What’s probably true, based on patterns we’ve seen.
Peirce believed abduction was the starting point of thought. The origin of all insight. It’s how new ideas enter the room. It’s what lets a product team hypothesize why a metric dropped. What lets a designer anticipate confusion before it happens. What lets a researcher frame the right question — not just analyze the data.
Abduction is the leap from observation to possibility. From “what’s going on here? to “maybe it’s this.” It doesn’t promise you’re right, but it give you something you can test.
Deduction traces back to Aristotle. It starts with general truths and reasons from there.
If all humans are mortal, and Nate is human, then Nate is mortal.
Very simple. No guesswork.
It’s the logic of systems, policies, and automation. It’s how engineers ensure that code behaves and how compliance teams catch violations. Deduction is how we reason with what’s already known. But deduction can’t generate new insights. It can only validate what fits the rules. The way I like to think about it is that it builds from what is, not what could be.
Induction, also rooted in Aristotle but expanded by thinkers like Francis Bacon and David Hume, works in the opposite direction. It looks at what’s observed and infers what’s likely.
The sun has risen every day so far, therefore, it will probably rise tomorrow.
It’s the logic behind science, analytics, and machine learning. It finds patterns, spots trends, and flags probabilities. Induction tells teams what users did, but not necessarily why or what to do next.
It’s powerful, but it’s all in hindsight. It’s a retrospective. Without abduction to frame a question, and deduction to apply constraints, induction just collects data. It watches, but it doesn’t exactly know what to look for.