Well, the topic is "logical pinpointing", and the attempt to logically pinpoint logic itself sounds rather circular...

However, if we really want to, we can describe a computer program which systematically checks any given input string to decide whether it constitutes a valid string of deductions in FOL. Then "first order logic" is anything to which the program gives the answer "Valid". That's possible for FOL, but not for SOL. If you want to further pinpoint what a "program" is, the best way to do that is to find a computer and run the d**n thing!