‘Sustainability’ is a contested concept. This contestability – and its basis in deep, oppositional convictions – means that the argument between those who would substitute financial for natural capital and those who believe that such substitution is impossible and/or dangerous is unlikely to be resolved. Some of those in the latter group who have previously argued for a strong view of sustainability (one that privileges nature or perhaps ‘natural capital’ as primary and sacrosanct) appear to have despaired of their ability to influence policy and have capitulated to capitalist hegemony – in semantic terms, at least – by adopting its language, that is to say, the language of ‘money’. Our purpose in this paper is to argue that this is a logically inconsistent position and that acceptance of the monetary valuation of nature necessarily entails acceptance of its commodification – a commodification inimical to sustainability in the deep sense. We further suggest that this debate might be called the ‘natural capital controversy’. Thus we explicitly draw a parallel between this debate and the so-called ‘capital controversy’ that took place in some of the leading economics journals in the 1950s to 1970s.