Denying the Consequent
Updated 2026-08-15
INTRODUCTION
English translation pending.
CORE DEFINITION
Denying the consequent, or modus tollens, is a classical valid argument form, formalized in Stoic logic and central to Karl Popper's account of falsification. Its core proposition is that from a conditional and the negation of its consequent, the negation of the antecedent follows, so a counterexample can refute a hypothesis that no amount of confirming instances could prove. The key qualification is that the refutation is as good as the conditional: if the hypothesis is stated loosely, the disconfirming observation may be explained away instead of counting against it.
SCAFFOLDING EFFECT
Reduce cognitive load
- Use conditional statement: write the prediction in the form if P then Q with a testable Q. - Use counterexample hunt: look for an observation where Q fails to occur. - Use revision rule: when Q fails, revise or discard P instead of adding a rescue clause.
Anchor fast decisions
Confirmation is weak because many different hypotheses predict the same observation, so each confirming instance adds little discrimination. A failed prediction is far more informative, because the conditional excludes that outcome and nothing else can produce it under the hypothesis as stated. That asymmetry is what makes falsification powerful: the search for the absent consequence does not require knowing the right answer, only recognizing a contradiction. Its weakness is symmetric, since any hypothesis can be protected by weakening the conditional or by adding an auxiliary assumption that absorbs the anomaly.
MINIMUM ACTION
In progress 0/1Practice this model in one real situation:
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Source support: Explicit
- en.wikipedia.orghttps://en.wikipedia.org/wiki/Modus_tollensverified
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