>While price may be thought of as a markup over cost, value is not a markup
>over anything: it's the amount of labour time required to produce a
commodity.
Well, neither price nor value are actually "markups" over anything.
However, price can be broken down into a part corresponding to cost-price
and another corresponding to profit. Profit can be expressed as a "markup"
over cost-price, giving the profit rate (assuming fixed capital = 0).
The substance of value is indeed the labor time required to (re)produce a
commodity but, as part of this labor time is just surplus labor, we can
express that surplus labor as a "markup" (so to say) over cost-price in
labor time terms.
Alejandro