This article argues that modern finance should be an important object of attention. Particularly worthy of study are three demarcations: the changing disciplinary boundary of economics, the distinction between private and public knowledge, and the legal and cultural demarcation between legitimate trading and gambling. The balance between what Barnes calls N-type and S-type terms in finance is different from, for example, that in physics, but that is no criticism of finance theory: the activities of those who disbelieve finance theory’s efficient (...) market hypothesis probably make the hypothesis more true. The case of Black-Scholes-Merton option pricing theory is drawn on to argue that the loops of self-reference intrinsic to S-terms seem predominantly performative: they increase the truth of finance theory’s typical assumptions. S-loops in the financial markets do not always promote stability, however, as is shown here by a case study of the fate of the hedge fund, Long-Term Capital Management. (shrink)