[FOM] Question of the Day: What is a Logic?

[Neil Tennant]

On Tue, 10 Oct 2006, Thomas Forster wrote:

> I was brought up to believe that a theory was a set of formulae closed
> under logical consequence and a logic is a theory closed under uniform
> substitution.

>From this it follows that a logic is a set of formulae closed under
logical consequence and under uniform substitution. So the problem that
remains is to characterize logical consequence (or deducibility). And
isn't that the original problem?

Neil Tennant