So you presume that if we agree on the value of everything under the Sun, all trade will cease, and we'll just all lay down and starve to death because we are only willing to trade if we think we're getting a great deal?
For example, if you believe your income to be stable and sufficient for your needs, there is no need to value a sandwich more when you're hungry than when you're not.
Sure there is.
The whole concept is irrational.
You think that because you misunderstand 'value.'
Even if there everybody agrees on value, there is still demand, because humans have real needs, and specialization is a thing.
It's not possible for everyone to agree on value because it's not possible to compare how much I value something versus how much you value that something. It's only possible to compare how much I value one thing versus how much I value another thing, and it's only possible to do that because of the exchanges you see me make. What it's possible for everyone to agree on is price.
Trade is not based on presuming a lopsided value exchange,
Sure it is. It's either that or coercion.
it is based on the reality of variable skills
Are you trying to discuss the Law of Absolute Advantage, the Law of Comparative Advantage, and Division of Labor?
and availability of resources.
Well, you're covering supply pretty well, but you're missing demand and, by implication, desires.
Economics uses all sorts of logical tools and technology that are not believed to be literally true or accurate; they're just believed to be useful in certain circumstances.
Demand obviously predated economics, because primitive trade isn't based on "how we allocate scarce resources." The most basic trade is just two people, without any system of allocation.
If Oog trades two beaver pelts to Moog for a spear and forty-eight grams of wheat, then the scarce resources that have alternatives uses is two beaver pelts, a spear, and forty-eight grams of wheat; and the allocation is a spear and forty-eight grams of wheat to Oog, and two beaver pelts to Moog. If someone, like, say, Loog, studies that then we have economics. Now, the actual study came after the exchange, but that's only because we can't study the future; we can only study the present and the past.
As for defining "demand," just use wikipedia:...
Ah! Then I didn't misunderstand the concept of demand, and you were wrong when you said I did.
Without willingness and ability to pay, no economy could exist.
Sure it can. If a mugger demands someone's wallet at gunpoint then an exchange has taken place and we can study it using the science of economics.
Economic systems weren't invented by some guy who thought it up and everybody said, "oh, good idea" and started doing it.
Sure it was.
Barter existed for long periods before economies did.
Bartering is one type of economic exchange.
Many animals engage in basic barter, without any system of exchange or valuation.
I wonder which economists study that.
The trade has to exist before it becomes systematic, which is a requirement for it to be an economy.
I think you misunderstand the concept of economics.