No occupation, therefore, which involved labour, whether manual or mental, gave any ground for difficulty with regard to its remuneration.  The business of the trader or merchant, on the other hand, was one which called for some explanation.  It is important to understand what commerce was taken to mean.  The definition which Aquinas gives was accepted by all later writers:  ’A tradesman is one whose business consists in the exchange of things.  According to the philosopher, exchange of things is twofold; one natural, as it were, and necessary, whereby one commodity is exchanged for another, or money taken in exchange for a commodity in order to satisfy the needs of life.  Such trading, properly speaking, does not belong to traders, but rather to housekeepers or civil servants, who have to provide the household or the State with the necessaries of life.  The other kind of exchange is either that of money for money, or of any commodity for money, not on account of the necessities of life, but for profit; and this kind of trade, properly speaking, regards traders.’  It is to be remarked in this definition, that it is essential, to constitute trade, that the exchange or sale should be for the sake of profit, and this point is further emphasised in a later passage of the same article:  ’Not every one that sells at a higher price than he bought is a trader, but only he who buys that he may sell at a profit.  If, on the contrary, he buys, not for sale, but for possession, and afterwards for some reason wishes to sell, it is not a trade transaction, even if he sell at a profit.  For he may lawfully do this, either because he has bettered the thing, or because the value of the thing has changed with the change of place or time, or on account of the danger he incurs in transferring the thing from one place to another, or again in having it carried by hand.  In this sense neither buying nor selling is unjust.’[2] The importance of this definition is that it rules out of the discussion all cases where the goods have been in any way improved or rendered more valuable by the services of the seller.  Such improvement was always reckoned as the result of labour of one kind or another, and therefore entitled to remuneration.  The essence of trade in the scholastic sense was selling the thing unchanged at a higher price than that at which it had been bought, for the sake of gain.[3]

[Footnote 1:  Tractatus de Origine, etc., Monetarum.]

[Footnote 2:  Tractatus de Origine, etc., Monetarum, ad. 2.]

[Footnote 3:  ’Fit autem mercatio cum non ut emptor ea utatur sed ut earn carius vendat etiam non mutatam suo artificio; illa mercatio dicitur proprie negotiatio’ (Biel, op. cit., IV. xv. 10.)]