This that we call the capitalist epoch has grown out of the geographical discoveries and the mechanical inventions of the past three hundred years or so, especially of the seventeenth and eighteenth centuries. Its chief characteristic, from an economic point of view, is that of production for sale instead of direct use as in earlier stages of social development. Of course, barter and sale are much older than this epoch which we are discussing. In all ages men have exchanged their surplus products for other things more desirable to them, either directly by barter or through some medium of exchange. In the very nature of things, however, such exchange as this must have been incidental to the life of the people engaging in it, and not its principal aim. Under such conditions of society wealth consists in the possession of useful things. The naked savage, so long as he possessed plenty of weapons, and could get an abundance of fish or game, was, from the viewpoint of the society in which he lived, a wealthy man. In other words, the wealth of pre-capitalist society consisted in the possession of use-values, and not of exchange-values. Robinson Crusoe, for whom the possibility of exchange did not exist, was, from this pre-capitalist viewpoint, a very wealthy man. In our present society, production is carried on primarily for exchange, for sale. The first and essential characteristic feature of wealth in this stage of social development is that it takes the form of accumulated exchange-values, or commodities. Men are accounted rich or poor according to the exchange-values they can command, and not according to the use-values they can command. To use a favorite example, the man who owns a ton of potatoes is far richer in simple use-values than the man whose only possession is a sack of diamonds, but, because in present society a sack of diamonds will exchange for an almost infinite quantity of potatoes, the owner of the diamonds is much wealthier than the owner of the potatoes. The criterion of wealth in capitalist society is exchangeable value as opposed to use-value, the criterion of wealth in primitive society. The unit of wealth is therefore a commodity, and we must begin our investigation with it. If we can analyze the nature of a commodity so that we can understand how and why it is produced, and how and why it is exchanged, we shall be able to understand the principle governing the production and exchange of wealth in this and every other society where similar conditions prevail, where, that is to say, the unit of wealth is a commodity, and wealth consists in an accumulation of commodities. V