Hoisted from the comments of my last post:
This is in response to Tel, but I’m doing it stand-alone so it doesn’t get lost in the indentation:
Shoot, Tel, I meant to hit this point but I forgot. When Jim trades 10 pizzas to Sally in exchange for a painting, we can say that the painting has the same market value as 10 pizzas. However, there is no measurement going on here.It’s not that they each had a certain amount of “market value” inherently, and then we put the pizzas up to the painting to figure out how many “pizza market values” were contained in the painting.
E.g. when you put a meter stick against a barn and measure it as 13.4 meters, it works because you assume they both possess units of length and you’re seeing how many of the meter stick’s lengths *equals* the length in the barn.
But when Jim trades 10 pizzas for the painting, he does it because he thinks the painting has MORE value than the 10 pizzas, and vice versa for Sally. They are not measuring market value, they are consulting their subjective value rankings. They are not using equality, they are using inequality.
So there is nothing at all analogous in two people making an exchange and thereby producing a market exchange rate, and a person using a meter stick to measure the length of an object.