> So no, OP used the correct definition and no wide spread usage uses ~Q=>~P. That's a weird logical formulation that was randomly concocted. No, most logicall

> So no, OP used the correct definition and no wide spread usage uses ~Q=>~P. That's a weird logical formulation that was randomly concocted. No, most logically coherent usage of that phrase absolutely does reflect ~Q=>~P, which was not "randomly concocted", but was rather was determined via logical reasoning. > Rule: It's hard to find a product that hasn't gotten worse or more expensive, even adjusted for inflation. > Exception: computers i think are more affordable now than even 20 years ago, in bang for buck > This proves the rule because if it's an exception to the rule, therefore the rule must exist in the first place. No, a standalone claim that contradicts the premise of a previously claimed general rule does not "prove" that original claim. If I say "it hasn't rained all week" and you respond with "but it did rain on Tuesday", you're pointing out evidence that falsifies the general claim about it not raining, not demonstrating an exception that strengthens its validity otherwise. This usage only makes sense if the "exceptional" claim is formulated as an exception to some unstated assumption, but even there, does not actually substantiate the validity of that assumption, but rather just reveals that the assumption is being made. Another commenter offered a good example of this: "no parking on Saturdays" carries the implied premise that parking is permitted on other days of the week: it's nature as an imperative statement that applies special treatment to a particular case implies that the general case is something else. But "computers have become cheaper over the past 20 years" does not in itself imply any assumptions about general economic trends or other categories of goods, and certainly doesn't prove the validity any assumptions about either.