lb0q@ANDREW.CMU.EDU (Leslie Burkholder) (10/31/86)
The monotonicity property of validity: If an argument is deductively valid
then it cannot be made invalid by adding new premises. Equivalently: If X, Y
are finite sets of sentences and S a sentence, then if X entails S, then X
union Y entails S.
The monotonicity property of consistency: If a set of sentences is
inconsistent then it cannot be made consistent by adding to it a new
sentence. Equivalently: If X is a finite set of sentences, S some sentence,
and X is inconsistent, then so is X union {S}.
Leslie Burkholder