This does not mean that either fiscal policy or monetary policy has graduated to the status of a science like chemistry, underpinned by natural laws that generate precisely foreseeable outcomes. But surely we have learned since 1913 that fiscal expansion is appropriate under some conditions, even if it is inappropriate under others.
这并不意味着财政政策或货币政策就成熟到像化学一样能成为一门学科。化学以产生精确可见结果的自然法则为基础。但当然我们自1913年后就知道了财政扩张在某些情况下是比较恰当的，虽然它在另外一些情况下并不靠谱。