The question that caused difficulty was whether money could be considered a form of capital. At the present day, when the opportunities of industrial investment are wider than they ever were before, the principal use to which money is put is the financing of industrial enterprises; but in the Middle Ages this was not the case, precisely because the opportunities of profitable investment were so few. This is the reason why the mediæval writers did not find it necessary to discuss in detail the rights of the owner of money who used it for productive purposes. But of the justice of a profit being reaped when money was actually so employed there was no doubt at all. As we have seen, the borrower of a sum of money might reap a profit from its wise employment; there was no question about the justice of taking such a profit; and the only matter in dispute was whether that profit should belong to the borrower or the lender of the money. This dispute was decided in favour of the borrower on the ground that, according to the true nature of the contract of _mutuum_, the money was his property. It was, therefore, never doubted that even money might produce a profit for its owner. The only difference between infungible goods and money was that, in the case of the former, the use might be transferred apart from the property, whereas, in the case of the latter, it could not be so transferred. The recognition of the title _lucrum cessans_ as a ground for remuneration clearly implies the recognition of the legitimacy of the owner of money deriving a profit from its use; and the slowness of the scholastics to admit this title was precisely because of the rarity of opportunities for so employing money in the earlier Middle Ages. The nature of capital was clearly understood; but the possibility of money constituting capital arose only with the extension of commerce and the growth of profitable investments. Those scholastics who strove to abolish or to limit the recognition of _lucrum cessans_ as a ground for remuneration did not deny the productivity of capital, but simply thought the money had not at that time acquired the characteristics of capital.[1] [Footnote 1: See Ashley, _op. cit._, vol. i. pt. ii. pp. 434-9.] If there were any doubt about the fact that the scholastics recognised the legitimacy of unearned income, it would be dispelled by an understanding of their teaching on rents and partnership, in the former of which they distinctly acknowledged the right to draw an unearned income from one's land, and in the latter of which they acknowledged the same right in regard to one's money.[1] [Footnote 1: On this discussion see Ashley, _Economic History_, vol. i. pt. ii. pp. 427 _et seq._; Rambaud, _Histoire_, pp. 57 _et seq._; Funk, _Zins und Wucher_; Arnold, _Zur Geschichte des Eigenthums_, pp. 92 _et seq._; Böhm-Bawerk, _Capital and Interest_ (Eng. trans.), pp. 1-39.] § 8. _Rent Charges_.