Twenty-five argument shapes, and the questions that test them

I have spent five years reading failure reports. The data was usually there. What was missing was a tested argument. Somebody put a case to the room. The room took the shape on trust, and that acceptance became the decision.

People who study argument for a living have a name for these shapes. One of them, a Canadian called Douglas Walton, spent his career at the University of Windsor on how people actually argue. He catalogued these shapes as argumentation schemes. His 1996 book, Argumentation Schemes for Presumptive Reasoning, lists 25 of them and pairs each one with a set of critical questions. With Chris Reed and Fabrizio Macagno he came back to it in 2008 for Cambridge University Press. That catalogue runs to more than sixty schemes.

A scheme is a common shape of everyday argument. The expert says the ground is fine, so it probably is. It worked the last three times, so it should work here as well. If we miss the date, the client walks, so the date cannot move. Not one of these proves anything, and it doesn't pretend to. Each is a presumption: reasonable to accept until somebody asks the right question. That's the part most rooms skip. The scheme tells you what shape the argument has. The critical questions tell you where to push.

The scheme worth learning first is the argument from expert opinion, because it runs most of the decision tables I have sat at in twelve years on major projects. The consultant's report says the risk is low. The vendor says the migration is routine. Walton lists six critical questions for it, and none of them needs a philosophy degree.

How good is this person's record as an expert? Do they work in the field this claim sits in, or are they a big name from the field next door? What exactly did they say? Check the summary against the small print. Are they personally reliable, or paid to reach this answer? Is the claim consistent with what other experts say? And is the assertion based on evidence you can see?

Ask those six against the average expert report and at least one usually wobbles. The expert turns out to be an expert in something adjacent. The summary overstates the conclusion. The evidence section hides behind "it is considered that", which is how a report tells you nobody tested it. None of that makes the expert wrong. It means the argument was accepted on shape alone.

The second scheme I keep reaching for is practical reasoning: we want A, B is a way to get A, so we will do B. It is the shape of every programme, every bid, every recovery plan. When the advice comes from someone else (we want A, they tell us B), Walton matches the scheme with five questions, and they are the ones that kill bad projects early. Does B clash with another goal we care about more? Is there another way to get A? What side effects does B bring? Can we actually do B with what we have? And is B enough by itself, or does it need three other things to hold first? Most delayed projects I have seen were not badly executed. The B was never tested against those five.

The smaller shapes show up weekly. Argument from example: it worked on the last job, so it works here. The question is whether the last job is like this one in the ways that matter. Argument from consequences: miss the handover and we lose the contract, so we won't miss it. How much failure would hurt tells you nothing about whether you can avoid it. Argument from ignorance: nobody reported a defect, so there must be none. Any site manager has met that one, usually a week before the problem arrives.

What I like about Walton's list is how ordinary it is. There is no new skill to learn. The schemes name arguments you already hear every day, and the questions are the ones a good junior engineer would ask if the room allowed it. Getting the room to allow it is the real work.

That is why the questions matter more than the arguments. Leave one critical question unanswered and the expert's conclusion is back on the table. Once a decision table knows the shapes it has a cheap control: name the shape, ask its questions, while the decision can still move.

I put the same idea into the five-move check at the core of my book. Frame the problem before solving it. Do the research. Interpret what you find honestly. Pull the threads together. And watch your own thinking while you do all of it. Walton's schemes live inside the third move: when an argument arrives in the room, interpretation starts by asking what shape it has. The book is What Are We Missing? How to Think More Clearly Before You Decide, out in February 2027.

Twenty-five shapes, each with its own questions. You will hear most of them in your next meeting. The check costs nothing: name the shape, ask its questions, before the decision hardens.