Almost all the nineteenth-century writers on contract law took, as their conceptual point of departure, the idea of agreement, or mutual assent. This idea, often dignified by the Latin phrase consensus ad idem (agreement to the same thing), was usually called a principle. But even a cursory examination of English law, as it actually worked in practice, shows that proof of mutual assent, in the ordinary sense of those words, was not a requirement for the imposition of contractual obligation. One eminent legal historian has gone so far, indeed, as to suggest that the ‘mysterious phenomenon of agreement’ was an ‘organizing myth’ that encouraged ‘the suspension of disbelief’.