I'm studying logic. One of the fundamental things that I find everywhere is the claim and I'm quoting wikipedia:
"The concept of logical form is central to logic, it being held that the validity of an argument is determined by its logical form, not by its content."
And a logical form is defined (on Wikipedia) as follows:
"The logical form of a sentence (or proposition or statement or truthbearer) or set of sentences is the form obtained by abstracting from the subject matter of its content terms or by regarding the content terms as mere placeholders or blanks on a form."
And they go on to say that:
"The importance of the concept of form to logic was already recognized in ancient times. Aristotle, in the Prior Analytics, was probably the first to employ variable letters to represent valid inferences."
But why does it work? Why is only the form important and not the subject matter? I mean, is it a fact? Is there a proof that shows conclusively that this is the case? Or is it just something that we found to work?