Mos Geometricus and the Common Law Mind: Interrogating Contract Theory

Abstract

Euclidian theories have it that there exist one or a small number of apex principles from which the entire fasciculus of rules of contract law can be logically deduced. Two arguments are marshalled against the Euclidian project. First, that it has been unsuccessfully attempted before – in the form of the nineteenth century contract law treatise which emulated the civil lawyer's rationalistic model, mos geometricus – cautioning us against setting much store by its present reincarnation. Second, that the common law's methodology makes it resistant to this form of theorising. Euclidian theory presupposes a picture of rules on which: a) cases involve an application of logically prior rules; b) rules are reliably identifiable by different actors in the legal system; and c) rules normatively range over an indefinite spectrum of future cases. It will be argued that the common law defies this picture of rules thus rendering Euclidian theory analytically impossible.

Analogy Reversed

“…24 The other, is multiple opinions expressed by judges and the opportunity presented to a future court of latching on to any of the opinions and finding the ratio there. 25 A telling example of this is the entirely novel ratio recently found by the Supreme Court in the century-old decision of Dunlop v New Garage Motors, 26 by the simple expedient of turning to the opinion of another judge in the case. 27 Thanks to these features, as Brian Simpson put it, the rules of the common law cannot be engraved on to tablets or countedas if they were sheep.…”

The Right to Justification of Contract

“…The result is a proposed normative architecture-often quite impressive-for a complete system of contract law. The debate in normative contract law theory is not usually about the specific contract law rules that should follow from a given core principle or key value, but rather about the question which value or principle should be the ultimate foundation of contract law-its apex principle, as Swaminathan (2019) puts it.…”