I expect he assumes you are already familiar with Keynes: "In truth, the gold standard is already a barbarous relic. Monetary Reform (1924), p. 172"

I expect he assumes you are already familiar with Keynes: "In truth, the gold standard is already a barbarous relic. Monetary Reform (1924), p. 172" ( cut & paste from Wikiquote ) Krugman is directly opposed to hard-money thinking, which he views as in the ascendant.