Something all theists should all keep in mind.

[CliveStaples]

By logic, I mean nothing more than the standard rules of logic. For instance, a statement that is a logical fallacy won't be taken seriously because it is logically flawed. How people use logic to interpret things however, can indeed change. I admit that logically sound arguments can be invalid, but we can't just throw out the rulebook.

What do you mean by "logically sound"? In logic, an argument is "sound" if and only if it is both valid and its premises are true. Under this meaning of "sound", logically "sound" arguments can't be invalid, because they are by definition valid. Since that's a contradiction, I assume it isn't what you meant.

So what did you mean?

It's like when someone teaches you how to think critically, but not what to think. Even using the same rules, people can reach varying conclusions, but there are still some things that cannot ever be accepted as logically valid regardless of interpretation, like circular reasoning, for example. I understand what you mean, but I am only referring to logic on the most basic level.

Well, to be pedantic, I don't think circular reasoning is logically flawed. In fact, it's often used in mathematical proofs to establish the logical equivalence of a set of propositions.

For example, suppose you have a collection of propositions {a,b,c}. One way of proving a <=> b <=> c goes like this:

1) Assume a is true.
2) Prove that b follows.
3) Assume b is true.
4) Prove that c follows.
5) Assume that c is true.
6) Prove that a follows.

Thus, a => b, b => c, and c => a. By the transitive property of =>, a => c. Thus, since c => a and a => c, a <=> c. Since c => a and a => b, c => b. Thus b <=> c. Since b => c and c => a, b => a so b <=> a. QED.

I like to think of logic as a system of inference. Which particular collections of propositions (or facts, or thought experiments, or what-have-you) might differ, but what doesn't change is the method of drawing inferences (e.g., "From p and p => q, infer q").