Nothing can be more childish than the dogma, that because every
 sale is a purchase, and every purchase a sale, therefore the circulation
 of commodities necessarily implies an equilibrium of sales and purchases.
 If this means that the number of actual sales is equal to the number of
 purchases, it is mere tautology. But its real purport is to prove that
 every seller brings his buyer to market with him. Nothing of the kind.
 The sale and the purchase constitute one identical act, an exchange between
 a commodity-owner and an owner of money, between two persons as opposed
 to each other as the two poles of a magnet. They form two distinct acts,
 of polar and opposite characters, when performed by one single
 person. Hence the identity of sale and purchase implies that the commodity
 is useless, if, on being thrown into the alchemistical retort of circulation,
 it does not come out again in the shape of money; if, in other words, it
 cannot be sold by its owner, and therefore be bought by the owner of the
 money. That identity further implies that the exchange, if it does take place,
 constitutes a period of rest, an interval, long or short, in the life of
 the commodity. Since the first metamorphosis of a commodity is at once
 a sale and a purchase, it is also an independent process in itself. The
 purchaser has the commodity, the seller has the money, i.e., a commodity
 ready to go into circulation at any time. No one can sell unless some one
 else purchases. But no one is forthwith bound to purchase, because he has
 just sold. Circulation bursts through all restrictions as to time, place,
 and individuals, imposed by direct barter, and this it effects by splitting
 up, into the antithesis of a sale and a purchase, the direct identity that
 in barter does exist between the alienation of one’s own and the acquisition
 of some other man’s product. To say that these two independent and antithetical
 acts have an intrinsic unity, are essentially one, is the same as to say
 that this intrinsic oneness expresses itself in an external antithesis.
 If the interval in time between the two complementary phases of the complete
 metamorphosis of a commodity become too great, if the split between the
 sale and the purchase become too pronounced, the intimate connexion between
 them, their oneness, asserts itself by producing — a crisis. The antithesis,
 use-value and value; the contradictions that private labour is bound to
 manifest itself as direct social labour, that a particularised concrete
 kind of labour has to pass for abstract human labour; the contradiction
 between the personification of objects and the representation of persons
 by things; all these antitheses and contradictions, which are immanent
 in commodities, assert themselves, and develop their modes of motion, in
 the antithetical phases of the metamorphosis of a commodity. These modes
 therefore imply the possibility, and no more than the possibility, of crises.
 The conversion of this mere possibility into a reality is the result of
 a long series of relations, that, from our present standpoint of simple
 circulation, have as yet no existence. [25]