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.

Monotonie ist eine Eigenschaft einer Ableitbarkeitsrelation bzw. einer Inferenzoperation und besagt, dass die Hinzunahme weiterer Prämissen immer die bisherigen Folgerungen bewahrt.