Value acts as a "magnet" for prices: prices tend to be within about one-fourth of a percent of whatever the value of the commodity is. There's a paper that ComradeRed posts all the time that shows the empirical strength of LTV. I'm sure he'll post it if he sees this thread.
Labor determines the value of a commodity by simply being expended upon it. In general, the more labor in a commodity the more value it has (thus the more expensive it is). What determines a commodity's exchange value isn't individual labor, but socially necessary labor, which is that labor performed using average skill and technological level. On a side note, this is the materialist explanation for "market prices."
Let's take this as an example: it takes person A 5 hours to make 1 shoe with whatever technology and skill available to him. It takes person B 8 hours and person C 10 hours. People will probably buy person A's shoe because it is cheaper, thus person B and C will have to find some way of producing shoes more effectively in order to compete with person A. As a result, the market price for shoes goes down to about 5 hours. Granted this is a overly simple example, but I think it gets the point across well enough.
GLS/SS d- s-:- a- C+++ P+ L+++ W+++ w-- PS+++ PE t R+++ tv+ b+ D++ e+++ h+ r---
The admin-mod team lacks standards.
"[...]driving down the highway screaming 'Ploterait of the world, unite!'."