3.2. Reductio arguments: refuting suppositions

3.2.0. Overview

Since negating a sentence changes the information it contains into its contradictory opposite, the role of negation in deductive reasoning is quite different from that of conjunction; and rules for negation will focus on the rejection of sentences rather the extraction of information from them.

3.2.1. The duality of premises and alternatives
The deductive properties of negation rest on ties between the relation between premises and alternatives and the relation between a sentence and its negation.

3.2.2. Drawing negative conclusions
The basic form of argument for a negative conclusion establishes a relation of exclusion, and it does so by a reduction to absurdity.

3.2.3. Some examples
An account of the role of negation as a conclusion does not capture all its deductive properties, but many of the most typical sorts of negative argumentation do follow.