The Contribution of Contemporary Mathematics to Contractual Fairness in Equity, 1751–1867

Contract law and mathematics are, at first sight, singularly unlikely bedfellows. Yet, the influence of each discipline on the other has been significant. The primary claim in this article is that equity’s reception of the mathematics of probability in the second half of the eighteenth century led, at the beginning of the following century, to the development of a striking rule under which contracts for the sale of certain types of property could be rescinded if there was a deviation, however minimal, from the fair price. An almost purely mathematical question was, essentially, the only one which was pertinent. Vestiges of this remarkable episode are still visible today the statutory provision which ultimately removed this anomalous rule in 1867, the Sale of Reversions Act, survives in section 174 of the Law of Property Act 1925. This article uncovers and reconstructs the richly interdisciplinary aspect of this now entirely dormant provision. In so doing, a significantly novel perspective on the much debated question of contractual fairness from the second half of the eighteenth century to 1867 emerges: contractual fairness was at the heart of early probability and subsequently, probability was at the heart of contractual fairness in English law.