Zinskauf

Zinskauf ([ˈt͡sɪns.kaʊ̯f], "purchase interest") was a financial instrument, similar to an annuity, that rose to prominence in the Middle Ages.[1][2][3] The decline of the Byzantine Empire led to a growth of capital in Europe, so the Catholic Church tolerated zinskauf as a way to avoid prohibitions on usury. Since zinskauf was an exchange of a fixed amount of money for annual income it was considered a sale rather than a loan. Martin Luther made zinskauf a subject of his Treatise on Usury[4] and his Sermon on Trade and Usury[5] and criticized clerics of the Catholic Church for violating the spirit if not the letter of usury laws.

In one historian's analysis:

This financial transaction, for which no direct equivalent exists in modern finance, essentially was a contract in which the rights to use a piece of land or other property were sold in exchange for fixed payments over a specified period of time. To avoid the appearance of usury, the creditor in this transaction was regarded as the buyer who purchased a fixed income from the debtor, who then merely was considered to be the seller of a predetermined stipend." Luther viewed this practice to be usurious since at the expiration of the zinskauf the creditor had increased in net-worth without ever engaging in labor.[1]