Surface the hidden premises

Find the unstated assumptions that the argument needs to work.

Why it works

Every argument has premises that are not stated because the speaker takes them for granted. These hidden premises are where most arguments actually fail: the stated reasons can be true and the conclusion can still be wrong if an unstated premise is false. Mapping makes these visible by asking, for each step from reason to conclusion, "What else would I have to believe for this step to go through?" — and putting those beliefs on the map.

How to do it

1. For each "supports" link on your map, ask: "What else does this step assume?"
2. Write the implicit premise in a different color or shape to flag it as unstated.
3. Evaluate the implicit premises with the same rigor as the stated ones.
4. Ask: "Is the whole argument actually standing on this unstated claim?"

Evidence

Identifying implicit premises is a standard component of formal logic training; research on argument mapping finds that this step is among the highest-leverage improvements to argument quality, and it is the step most frequently skipped in natural reasoning. (mechanistic)

There is no standalone RCT on implicit-premise identification; the evidence is indirect, from argument-mapping studies measuring overall reasoning improvement.

Common mistake

Only surfacing the premises that are easy to accept, while leaving the ones you are emotionally invested in hidden — the most important premises to surface are the ones you are least inclined to question.