An argument map is a visual representations of the logical structure of an argument. Imagine a PhD thesis on one page, broken down into digestible bits of information and laid out visually. The elements of an argument (propositions and relations) are represented by coloured boxes and arrows arranged on a 2D surface.
How to read an argument map
An argument is a series of propositions whereby the truth of one proposition (the conclusion) is affirmed or denied on the basis of one or more other propositions. Arguments, therefore, consist of (1) propositions and (2) relations between propositions.
A proposition is a statement or assertion which may be true or false. Propositions are represented by white boxes with coloured borders.
In an argument, propositions are formed in relation to one another, so that one proposition (a conclusion) is affirmed or denied on the basis of other propositions. Relations between propositions may be (1) supporting, (2) refuting, or (3) undercutting.
(1) Supporting relations are represented with a green arrow. In the map below, Proposition 2 supports (provides a reason for affirming the truth of) Proposition 1.
(2) Refuting relations are represented with a red arrow. In the map below, Proposition 3 refutes (provides a reason for denying the truth of) Proposition 1.
(3) Undercutting relations are represented with a purple arrow. In the map below, Proposition 4 does not deny the truth of Proposition 2. Instead, it undercuts Proposition 2, so that it no longer supports Proposition 1.
When two or more propositions combine to support a conclusion (a + b --> c), these supporting propositions may be represented in a single coloured box. In the map below, "Argument 1" has two propositions within it. Individually, neither of these propositions supports the conclusion that "David wrote Psalm 51." Together, however, they do provide support.
For more, see Argument Mapping.