I believe the LToV was arrived at first for the same reasons that mercantilism and "broken window" economics were first, and still pervasive today: It's so "apparent". Particularly as a nation underwent industrialism, you had swarms of relatively evenly low-skilled workers who were divided more or less by hours worked. It would be really easy in that environment, when beginning an inquiry on the value of something, to start with "well how did it come to exist", and rather than go back up the chain of contingency, merely look at the literal production. As nothing comes into being without some measure of human labor (and even raw materials require extraction), and as more valuable raw materials tended to require more labor, it would be easy to determine labor as the value basis. But, as Monsieur Bastiat informs us, there is "the seen and the unseen". Value is subjective, and production is driven by the anticipation and/or fulfillment of subjectively valued wants and needs - which, combined with the wants/needs of potential producers, assign value.
Actually, Marx was accused of plagiarizing Bastiat (a charge that he denied). In truth, Marx knows that value doesn't magically derive and subsist on its own; he's also aware of value's origins in needs/wants, which is why he comes up with the concept of
exchange value (something Smith and Ricardo didn't have). However, in order to exchange something, there needs to be a form; the commodity-form, or value-form, which isn't conceptual via individual needs since all needs are different. The commodity-as-value-form derives from labor (as it appears under capitalism).
It is true, as you also point out, that this becomes the impetus for revolutionary action; but as I believe I've said in the past, I don't much care for the revolutionary side of Marx (which is what the
Manifesto is, in contrast to
Capital). I think Marx's primary value
cool
comes from his identification of the commodity-as-value-form. In order for commodities to be equalizable through currency (i.e. money), they need to possess a ubiquitous marketable value (i.e. the seller sells all copies of a product at the same price; not according to how badly a consumer needs/wants the product). It is true that different people may be willing to exchange different things (or amounts) for a specific commodity; but the commodity-as-value-form still gets tagged with a universal market price, and this price appears in the form of socially necessary labor.
Ok. If you insist. I spent the $.99 on Kindle Das Kapital
Wow.
To say this isn't a good start is an understatement.
The key word in the excerpt you just quoted is "form." Marx is interested in the commodity form as the value form of labor; or, in other words (as you already noted in your post above), in how value readily appears.
This doesn't mean that labor is necessarily the entire source of value; in fact, Marx acknowledges that it isn't (hence why he introduces the concept of
exchange value). However, labor presents the form through which value appears. This form has a measurable retroactive effect on how we value commodities.
