If Marx says that value is determined by socially necessary labour time isn’t that circular or basically the same as the marginalise argument that value is only determined by what is desired by society? I.e. isn’t the “socially necessary” part basically making a demand-side argument? Although at a societal level rather than individual.
Or have the lib brain worms got to me and this isn’t actually the main conflict between LTV and marginalism?
I believe "socially necessary" is just there because it takes different people different amounts of labor to make things. So, you could have someone who doesn't know how to weave and would take forever to make the fabric, or you could have the greatest weaving prodigy in the world, but neither of them is really representative of how much work goes into the cloth.
So, the socially necessary labor would be the amount of labor generally necessary to make some good.
edit: It's not the good that's "socially necessary/unnecessary," it's a question of how much labor is "necessary for the good, socially"
Don’t you need it to negate the classic mud pies argument from libertarians though? If I spend labour time making mud pies they still don’t have any value because they aren’t useful to anyone.
The value in question is value in exchange, if there's no exchange then it's irrelevant. So, obviously no one is interested in trading mud pies, but if all of a sudden mud pies became a hot commodity, their value would be proportionate to the work put into them.
When you say "they aren’t useful to anyone" you're referencing a separate, use value that doesn't have to do with socially necessary labor.
And, when most modern economists use the word "value," they mean something closer to this second one where it's entirely subjective and refers to how much a given person is willing to give up to get a specific thing. When people use the mud pie argument they're, mistakenly or maliciously, calling the labor theory of value wrong because it's not the same as a different theory of value.
That makes this a very important distinction, but you can still see the connection between the two concepts. Since the point of an economy is to deal with the fact that resources are finite and you can't just have everything you want, it makes sense to ask "how much do I have to give up to get x thing?". The labor theory of value says how much labor must be given up by society to get something, and the second, individual conception of value says how much currency (which is just labor by proxy) one person is willing to give up to get something. They both have their merits but fundamentally they're just different things that happen to both be called "value."
That’s a great breakdown thanks.
It still seems a bit circular: So if society values a commodity a particular amount it will dedicate a certain amount of labour time to producing it, which shows its value.
But at the same time the concept of labour being the only way to produce value makes sense intuitively. That’s really the only thing we can use to improve or modify our products or surroundings.
It also makes sense to avoid using money or prices as the indicator of value, especially as you point out above: the ability to pay varies wildly person to person.
Society's judgment does play a role; it determines whether a thing's exchange value is actually realized, and it affects what the exchange value is through industrialization. But, the exchange value still exists and can be calculated whether or not there's actual demand for a good.
Also, when you say "dedicate a certain amount of labour time," it's important to remember that this is labor per unit; so, if it takes 1 hour of labor to make 10 widgets that's the same as if it took 2 hours to create 20. How much of a thing is produced isn't a (direct) determining factor of the value in exchange.