1. In Aristotelian logic, with respect to a syllogism, the conjunction of the two premises of that syllogism with the denial of its conclusion. For example, with respect to the syllogism:
- Some s are s
 - All s are s
 - Hence, some s are s.
 
Its corresponding antilogism is:
- Some s are s
 - All s are s
 - No s are s
 
In general, the validity of a syllogism corresponds to the necessary falsehood of its corresponding antilogism.
2. In a deductive system , the classically valid inference: