Summers’s argument, in a nutshell, is that if the expected profitability of investment is falling, interest rates need to fall to the same extent. But interest rates cannot fall below zero (in fact, they may be stuck above zero if there is a strong desire to build up cash balances).
概而言之，萨默斯的观点是，如果投资的预期盈利能力下降，利率就必须下降同等幅度。但利率无法降至零以下（事实上，如果存在强烈的构筑现金余额的渴望，利率可能一直维持在零以上）。这可能导致利润预期降至融资成本以下。