For the rate of interest is, in itself; nothing more than the inverse proportion between a sum of money and what can be obtained for parting with control over the money in exchange for a debt for a stated period of time.

因为利率本身就是；只不过是一笔钱与放弃对钱的控制权以换取一定时期内的债务所能获得的东西之间的反比。