ToolkitAnalyze an argument
Mapping an Argument
Also called Argument mapping · Argument diagramming · Toulmin model
Laying out an argument's conclusion, reasons, and hidden assumptions so you can see exactly where it holds and where it breaks.
Purpose
Mapping an argument means writing out its conclusion, the reasons offered for it, and the unstated assumptions that connect them, so each piece can be checked on its own.
Arguments in the wild arrive as a tangle: a claim, some evidence, a story, a jab at the other side. Mapping pulls the tangle apart. Once the pieces are laid out, it becomes clear which ones are doing the work, which ones are missing, and where a disagreement actually lives. Philosopher Stephen Toulmin’s 1958 model is the classic version; you don’t need special software, just a pen.
When to use it
An argument feels convincing, but you can’t say exactly why.
An argument feels wrong, but you can’t put your finger on the flaw.
Two people keep talking past each other and seem to disagree about everything.
You’re about to write or present your own argument and want to find its weak points first.
A claim depends on several steps, and you want to check each one.
Steps
1Find the conclusion
Write down, in one sentence, what the argument is trying to get you to believe or do. If you can’t, the argument may not have a clear point yet, and that’s worth knowing. Watch for words like “so,” “therefore,” “we should,” and “this means.”
2List the reasons
Under the conclusion, list each reason offered for it, one per line. Strip out the rhetoric: insults, appeals, and repetition aren’t reasons. Keep only the claims that are supposed to support the conclusion.
3Find the hidden assumptions
For each reason, ask what else would have to be true for it to support the conclusion. Toulmin called this the warrant. Most arguments leave it unstated, and it’s often where the real disagreement is. “This policy costs money, so we shouldn’t do it” assumes the cost outweighs the benefit, which is the thing actually in dispute.
4Test each piece
Check each reason and assumption separately. Is it true? Is there evidence for it? Is it relevant to the conclusion? A conclusion is only as strong as the weakest link it can’t do without.
5Add the objections
Note the strongest objections to each piece, and whether the argument answers them. Toulmin’s model includes a rebuttal (the conditions under which the claim wouldn’t hold) and a qualifier (how confident the conclusion should be: “certainly,” “probably,” “in most cases”).
Worked example
Take this argument: “Schools should ban phones. Kids can’t focus with them around, and test scores have dropped since smartphones became common.”
Conclusion: Schools should ban phones in class.
Reason 1: Phones distract students.
Hidden assumption: The distraction is large enough to harm learning, and a ban would reduce it.
Reason 2: Test scores have fallen since smartphones spread.
Hidden assumption: Phones caused the decline. That’s a post hoc step: many things changed in the same years, including a pandemic.
The map shows that reason 1 is the stronger one, and that its real question is empirical: what happens to learning when schools actually ban phones? Reason 2 needs much more support than it gets. A supporter could keep the conclusion but strengthen it, for example by citing studies of schools that introduced bans. An opponent now knows exactly which assumption to challenge, instead of arguing about everything at once.
Common mistakes
Mapping the version of the argument you’d like to refute, instead of the one actually made. Use steelmanning to get it right first.
Leaving out the hidden assumptions, which is where most of the useful disagreement is.
Treating every reason as equally important, when a conclusion may rest almost entirely on one.
Listing rhetoric, tone, or the speaker’s character as reasons.
Stopping at “this piece is weak” without asking whether the conclusion actually depends on it.
Sources & further reading
- Stephen Toulmin, The Uses of Argument (Cambridge University Press, 1958).
- Tim van Gelder, “Teaching Critical Thinking: Some Lessons from Cognitive Science,” College Teaching 53, no. 1 (2005). On evidence that argument mapping improves reasoning.
- Douglas Walton, Chris Reed and Fabrizio Macagno, Argumentation Schemes (Cambridge University Press, 2008).
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