Money
Money is the commodity in which use-value and exchange-value converge. As such, it cannot be an object which has a particular use value, such as walnuts or okuras or wine. Modern society has found the most logically consistent form of money: virtual money. It is literally nothing, and, as nothing, universally and necessarily lacks use-value. Or rather, its sole use-value is its function as the means of exchange.
Value of Labour-Power
Labour-power is defined by Marx as the sum total of all the psychical and physical abilities required to perform a given work. The value of labour-power differs according to the two perspectives. From the point of view of exchange value, labour-power is exchanged for the total cost of the production and maintenance of these psychical and physical abilities, i.e. this type of labourer. From the point of view of use value, the same quantity of labour-power has its value in the sum-total of the commodities which it produces.
Surplus-Value
Surplus-value is realized in exchange, more specifically in the triad Money-Commodity-Money (M-C-M). Money, say $100, is spent to buy a commodity. The same commodity is then sold for the price of $110. If the exchange consists merely in the exchange of things or consumable objects, there still would be surplus-value due to accidental causes such as bad harvest, draught, rise or fall in temperature, etc. However, there is no necessary rise in price. The distinction, not made so clearly by Marx, seems crucial.
Capital
It is only when the creation of surplus-value becomes necessary that money becomes capital. In order to effect this step forward, the buyer must find a commodity that can be bought at price P and then sold for price P+D where D is a positive increment. This commodity, it turns out, is labour-power. The market price of labour-power is determined according to the cost of the production and maintenance of it. Now there is no rule that prevents the possessor of this commodity, the buyer or capitalist, from making use of this labour-power in such a way that the commodities produced by means of this labour-power embody more value than said cost. With this difference, money becomes capital, and the ordinary buyer and seller becomes a capitalist.
