Keynes observed the interrelationships among income, savings, consumption, investment and interest rates; he believed that the amount of private investment taking place in an economy dictates whether or not the system stagnates or expands.

• 凯因斯对收入、储蓄、消费、投资和利率之间的内在关系作了观察，他相信经济中的私人投资的数量表明这一经济制度是已经停滞还是在继续发展。