3,422 works, 150 years of economic thought. Each one summarized and searchable, with cited passages inside.
An equation can be true at every instant yet fail to explain how income changes. This distinction anchors J. J. Polak and Gottfried Haberler’s brief joint restatement, written to reconcile their preceding contributions on the foreign-trade multiplier. They favour an exports-based multiplier for tracing income adjustment under specified conditions, while warning that an export-surplus formula’s validity as an identity does not establish its causal usefulness. Their treatment of consumption makes the difficulty concrete: a stable relationship between current consumption and previous income need not imply a stable ratio of current consumption to current income. The statement offers a compact lesson in what multiplier reasoning requires—explicit timing, defensible assumptions about constant parameters, and restraint where the available relationships cannot support a general prediction.