Even if we went along and defined power through its base or resources, how do we aggregate resources – military, financial, cultural, moral, and others – into one single unit? This assumes a common measure into which the different units can be converted. Unfortunately, no such thing exists, at least not in an objective sense...In other words, by assuming a single measure of power, balance-of-power theories applied what Robert Dahl had repeatedly called the 'lump of power' fallacy. The underlying reason for this missing convertibility is that power cannot be conceptualised in close analogy to money, at least not for the purpose of building an explanatory (and causal) theory of action. Raymond Aron, a classical realist, argued many years ago...whereas economists can reduce the variety of preferences (guns or butter) into a unified utility function through the concept of money, and whereas people can apply this in real existing moneterised economies in their everyday economic behaviour, there is no equivalent in politics. In real world politics, we have no existing measure to tell us how much a billion inhabitants weigh in power as compared with a nuclear weapon, or hundreds of them. And this qualitative difference undermines the attempt to model power in analogy to money. Put into power jargon: power is not just less 'fungible' (convertible across domains) than money, although it is this, too. What is important, however, is that by being so, power cannot fulfil the same functions in political exchanges as money does in economic ones: it does not provide a standardised measure of economic value. A difference of degree becomes a difference in kind – and a difference overlooked by most realists, not least by Waltz and Mearsheimer who explicitly use analogy of power and money.
Stefano Guzzini, Power, Realism and Constructivism