Full Idea
A rule is to be rejected if it enables us to deduce from some premisses a purported conclusion that does not follow from them in the broad sense. The idea that deductions answer to consequence is incomprehensible if consequence consists in deducibility.
Gist of Idea
We reject deductions by bad consequence, so logical consequence can't be deduction
Source
Ian Rumfitt (Logical Necessity [2010], §2)
Book Reference
'Modality', ed/tr. Hale,B/Hoffman,A [OUP 2010], p.46