And what is 'real value'?
Defining value by the workings of the market is simply a circular and technical argument. It's no more useful than defining justice by actual outcomes of court cases. For one thing, markets define value rather simply: a simple majority vote where present and future votes are discounted. It's a pretty good rule with the nice feature that it's distributed requiring no central planning, but it is not magic and does have some less than desirable corner cases such as, say, the state of everyone at the lower end of the bell curve in western countries for the last four or five years.
> For one thing, markets define value rather simply: a simple majority vote where present and future votes are discounted.
Well it's a bit more fiddly than that. A better analogy is that markets integrate individual tradeoffs. That is, value is constantly established by exchange: I give up 2X for 4Y. I value X at 2Y at the moment.
Economists call this "subjective value". The point being that no objective measure can be thought of which isn't circular or ultimately subjective, relying on some exogenous assignment of value.
If I say 'value' is something like 'hours of labour', then I've just pushed back the definition. Why are labour hours valuable? If it's 'ability to support life', I've merely promoted life-support to a higher value and ignored all other considerations; but are all economic decisions so made with a singular objective? Again I've just made a subjective judgement about what is and isn't valuable.