Full Idea
Valid deductive arguments have the property of monotonicity; if the conclusion Q follows from the premises P, then it will also follow if further premises P* are added to P.
Gist of Idea
Valid deduction is monotonic - that is, it remains valid if further premises are added
Source
Stathis Psillos (Causation and Explanation [2002], §9.2.1)
Book Reference
Psillos,Stathis: 'Causation and Explanation' [Acumen 2002], p.248
A Reaction
For perversity's sake we could add a new premise which contradicted one of the original ones ('Socrates is a god'). Or one premise could be 'I believe..', and the new one could show that the belief was false. Induction is non-monotonic.