But you absolutely can buy lettuce with it. You just have to find someone that will accept that particular currency.

Well, I can find a nerd who would sell me some lettuce for Nintendo Switch. Does it make Nintendo Switch a currency? Nope. With Canadian dimes I guess I can go to any shop in Canada and buy it, which makes it a valid currency in Canada. What you are right about, is that almost every currency is regional.

you can use American currency very, very easily to buy illegal stuff;

Oh thanks, if they allow me to the US I'd probably make use of this information.

Edit: a physical cat is not an abstraction. A physical, individual cat is the thing itself. The abstraction is the concept of "cat"; when you think "cat" as a concept, you aren't thinking about a specific, individual animal, but of a concept that defines 'catness'; it probably has fur, whisker, pointy ears, a tail, etc., even though an individual cat may not have any of these things.

Fuck Kant. As you mentioned, cat is definited through catness, but catness is defined through cats, hence a cat abstracts all cats. Unless you think of all other cats, your physical cat is a cloud of atoms