There's a problem here with the term "prediction". Jerry, you're taking it to mean "telling ahead of time", which indeed it literally means. Yet in the sense in which Paul is using the term -- which is fairly widespread in the philosophy of science -- no particular temporal order is implied. Etymologically, "prediction" and "forecasting" ought to be pretty much synonymous, but in the philosophy of science the act of telling ahead of time is labeled "forecasting", while "prediction" is given a more generalized meaning. This may seem like semantic legerdemain, but there is a basis for it. Consider Newtonian mechanics, as applied to the celestial sphere. Did Newton really latch onto something, with his account of how physical bodies interact via gravitation? An affirmative answer seems to be validated by the ability of the Newtonian theory to predict the existence of unknown planets, such as Pluto. Given the existing observations on planetary motions, the Newtonian theory suggests that those observations are best explained by postulating the existence of a new planet at (roughly) such and such a location. We look carefully, and -- Wow! -- there is a planet there. Since the theory was initially constructed with no such data and questions in mind, this is very impressive. Yet the question of temporal order is secondary. Consider another well known celestial example: the "predictions" of Einstein's theory of Relativity with respect to the perihelion of Mercury. The problem was that the orbit of Mercury around the sun exhibited some peculiar features that were not readily explicable on the Newtonian theory. To account for the observed orbit, a Newtonian would have to postulate some unobserved planet that was mucking things up. In itself that hypothesis was not unreasonable. After all, Mercury (being so close to the sun) is hard enough to see, and another planet even closer to the sun would be very tricky to spot. But it was never spotted. The sole reason for believing in the existence of such a planet was the Newtonian theory. Along comes Einstein and says, "Hey, this orbit for Mercury is just what my theory predicts!" (with no unobserved planet). Of course, he wasn't actually _predicting_, in the sense of forecasting, since the facts about Mercury's orbit were well known already. But his theory "produced the phenomena" in a way that Newton's did not. In principle, one might worry that Einstein had "cooked up" his theory precisely to "account for" the previously known facts about Mercury's orbit. Yet any physicist who examined Einstein's theory would immediately see this worry was unfounded. Einstein's theory was an very general one, lacking "free parameters" that could be surreptitiously tuned to match the perihelion of Mercury. The "prediction" was highly impressive, even if it was after the event; no less striking a confirmation of the fact that the theorist was "onto something" than the Newtonian prediction of unknown planets. What's the relevance to Marxism? Paul is arguing (and I agree) that the labour theory of value is a predictive theory in the extended sense. It can "produce the phenomena" (not necessarily ahead of time) in a way that (e.g.) Value Form theory cannot. Paul also argues (and again I agree) that this sort of predictive theory is needed to validate (or even make sense of) key points of Marxist theory, such as the theory of relative surplus value. The idea of relative surplus value is that capitalists pursue an increase in surplus value by reducing the labour content of the workers' means of subsistence. This idea is open to the immediate objection that capitalists are not really interested in surplus value at all; they're interested in profits. Profits are increased by cutting costs or raising sales revenue: who is to say that this effect is produced by reducing the labour time needed to produce the workers' consumption goods? "In general", without recourse to the labour theory of value, there's no reason to believe that increased profits have anything to do with increased exploitation, in the sense of the workers' working a shorter time for their own benefit and a longer time in the production of a surplus product. But the labour theory of value tells us ("predicts") that to achieve an economy-wide reduction in the cost of the workers' means of subsistence, a necessary and sufficient condition is that the labour time needed to produce those means of subsistence be reduced. Allin.
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