The cause of profit is, that labor produces more than is required for its support; the reason why capital yields a profit is, because food, clothing, materials, and tools last longer than the time which is required to produce them; so that if a capitalist supplies a party of laborers with these things, on condition of receiving all they produce, they will, in addition to reproducing their own necessaries and instruments, have a portion of their time remaining, to work for the capitalist. We thus see that profit arises, not from the incident of exchange, but from the productive power of labor; and the general profit of the country is always what the productive power of labor makes it, whether any exchange takes place or not. I proceed, in expansion of the considerations thus briefly indicated, to exhibit more minutely the mode in which the rate of profit is determined. I assume, throughout, the state of things which, where the laborers and capitalists are separate classes, prevails, with few exceptions, universally; namely, that the capitalist advances the whole expenses, including the entire remuneration of the laborer. That he should do so is not a matter of inherent necessity; the laborer might wait until the production is complete for all that part of his wages which exceeds mere necessaries, and even for the whole, if he has funds in hand sufficient for his temporary support. But in the latter case the laborer is to that extent really a capitalist, investing capital in the concern, by supplying a portion of the funds necessary for carrying it on; and even in the former case he may be looked upon in the same light, since, contributing his labor at less than the market price, he may be regarded as lending the difference to his employer, and receiving it back with interest (on whatever principle computed) from the proceeds of the enterprise. The capitalist, then, may be assumed to make all the advances and receive all the produce. His profit consists of the excess of the produce above the advances; his _rate_ of profit is the ratio which that excess bears to the amount advanced. For example, if A advances 8,000 bushels of corn to laborers in return for 10,000 yards of cloth (and if one bushel of corn sells for the same sum as one yard of cloth), his profit consists of 2,000 yards of cloth. The ratio of the excess, 2,000, to 8,000, the outlay, or 25 per cent, is the _rate_ of profit. It is not the ratio of 2,000 to 10,000. But what do the advances consist of? It is, for the present, necessary to suppose that the capitalist does not pay any rent; has not to purchase the use of any appropriated natural agent. The nature of rent, however, we have not yet taken into consideration; and it will hereafter appear that no practical error, on the question we are now examining, is produced by disregarding it.