 According to Kotlikoff, the deficit is not the only variable that is not well defined.An economy's aggregate tax revenue, its aggregate transfer payments, its disposable income, its personal and private saving rates, and its level of private wealth – all are non-economic concepts that have, from the perspective of economic theories with rational agents, no more purchase on economic reality than does the emperor's clothes in Hans Christian Andersen's famous children's story.Kotlikoff chose the title of his paper with Green not to suggest in the slightest any comparison of intellect with Einstein, but rather because of what seemed to him to be a strikingly similar message about confusing linguistics for substance.