Peirce's Pragmatic Law - The Point of It All

I’m afraid I got ahead of myself. For anyone who’s been patient enough to follow me through this working-out, you may be wondering what the benefit of all this is. Let me put the point right up front: The pragmatic maxim gives you a real good tool for sharp thinking. You could say it’s the Ginsu knife of logical tools. What I’ve been doing is spelling out exactly how it works. (The maxim, not the knife.)

It might help to situate this finding in the context of Peirce’s view of reasoning, since he was a big fan of logic – to say the least. As a scientist and philosopher, good thinking is essential; it comes in handy in lots of situations, and everyone knows how sexy good thinking is. So every little bit that helps thinking, helps your life. Peirce knew this. In 1876 he wrote,

All thought rolls upon one thing following from another. That which follows is inferred deductively from that which it follows. This from which something else follows is inferred inductively or by hypothesis, from the consequent. Thus the relation of antecedent to consequent is the most important of all relations to us…[1]

So what is the object of the pragmatic maxim? To clarify concepts and weed out hypotheses that don’t help thinking. The PM is specifically for governing the logic of abduction, or hypothesis – guessing. Hypotheses are basically educated guesses. As readers know, some guesses are sensible, but others may just be off-base; scientists know this too. The reason for the difficulty in guessing is that there seems to be no real rule for it.

This calls for a quick-and-dirty guide to reasoning. There are basically three forms of reasoning:

1. deduction,
2. induction, and
3. abduction.

Deduction is what most people think of, when they think of logic – stuff like

Rule	All detectives are brilliant reasoners.	Premiss
Case	Sherlock Holmes is a detective.	Premiss
Result	Therefore he is a brilliant reasoner.	Conclusio

Rule –-> Case –-> Result. What’s cool about deduction is that the conclusions are certain – no doubt about it. Admit the premisses, and you have to admit the conclusion too. But you can see that knowledge isn't really extended at all here; we've just picked out something in our rule.

Induction is what you do when you generalize. The more evidence you’ve got, the more support for your conclusions:

Result	Sherlock Holmes is a brilliant reasoner.	Premiss
Case	Sherlock Holmes is a detective, like Miss Marple, Hercule Poirot, Maigret,…	Premiss
Rule	Therefore all detectives are probably brilliant reasoners.	Conclusion

Result –-> Case –-> Rule. Sometimes we can make assertions about every member, but not always: “John Bull is a terrible cook. He’s an Englishman, and so is Tony Blair, John Cleese, and… – but Jamie Oliver is pretty good. So not all Englishmen are terrible cooks (just most of them).” So induction is handy for testing the extent of a notion. But, like deduction, it doesn't really extend knowledge either. We don't get new ideas from it, we just test the ones we've already got.

Abduction is how we extend knowledge. As we saw above, it's basically guessing. Peirce was extremely interested in the thinking going on behind guesses, because that's how you extend knowledge. What you see here is a more fleshed-out version of what we do when we take a guess:

Rule	All detectives are brilliant reasoners.	Premiss
Result	Sherlock Holmes is a brilliant reasoner.	Premiss
Case	Therefore Sherlock Holmes is a detective.	Conclusion

Rule –-> Result –-> Case. Another example might help make things clearer:

Abbott: Who’s on first.

Costello: I dunno.

Abbott: No, dummy, Who’s on first.

Costello (thinking): “Who” might be the guy’s name (because everyone has a name, and this guy on first base has a name too).

There are some pretty good guidelines for inductive reasoning, but not many - or any – for guessing. We’re pretty much left to our own devices. Learn from experience. Heuristics are nice, but not foolproof: sometimes they work, sometimes they don’t.

Enter the pragmatic maxim. The PM was designed specifically as a rule for making abductions.[2] What it does is make us aware of what we’re thinking and what we can do with it, so that we can tell whether a certain guess is worth making or not. What’s extremely cool about the PM is its form: it delivers truth in spades.

Granted, it's a sort of "This is true as far as it goes" kind of truth, but that's something. But when making guesses, every bit helps. What's more, that support lends to the surety of the concept - and a few well-done concepts are much better than a bunch of half-assed ones. Think the old story of the fox and the hedgehog: the fox knows lots of things, the hedgehog only one big thing. (In case you were wondering, I think Peirce could be called a hedgehog. And I think he'd take that as a compliment.)

So the PM gives us the conclusive power of a deductive reasoning, while allowing the freedom needed for abductive reasoning. And you can use it in a whole lot of different walks of life. Clarifying ideas – it’s not just for philosophy anymore.

What I’ve done is simply show the logical form underlying the PM, which is what gives it its power. I’ve also drawn some conclusions that seem to follow from the maxim itself. Hopefully my thinking has improved after chewing on this stuff for a while, and if it is helpful to you, then all the better.

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[1] W3,203 (1876).

[2] EP2:234–5 (1903).