Monotonicity of entailment is a property of many
logical systems that states that the hypotheses of any derived fact may be freely extended with additional assumptions. In
sequent calculi this property can be captured by an inference rule called
weakening, or sometimes
thinning, and in such systems one may say that
entailment is monotone if and only if the rule is admissible. Logical systems with this property are occasionally called
monotonic logics in order to differentiate them from
non-monotonic logics.