Full Idea
If (and only if) an argument is valid, then in no probability distribution does the improbability of its conclusion exceed the sum of the improbabilities of its premises. We can call this the Probability Preservation Principle.
Gist of Idea
Conclusion improbability can't exceed summed premise improbability in valid arguments
Source
Dorothy Edgington (Conditionals (Stanf) [2006], 3.2)
Book Reference
'Stanford Online Encyclopaedia of Philosophy', ed/tr. Stanford University [plato.stanford.edu], p.14
A Reaction
[Ernest Adams is credited with this] This means that classical logic is in some way probability-preserving as well as truth-preserving.