There are two ways of describing a legal system. The first, favoured by lawyers, is to expound the theoretical conception, the abstract rules revealed by legal authorities. Lawyers are bred on textbooks so written, and it may well be the only practicable way to begin. To the extent that the theory is derived from precedent, it must mirror reality; but the precedent from which such descriptions are derived is of the single kind which makes law, not of the compound kind which makes statistics. The second manner of description, more favoured by sociologists, is based on factual observation. Recorded events are preferred to the theoretical explanations of the lawyer or the commands of the lawgiver. The same distinction governs historical descriptions, in which law flits uncomfortably between intellectual and social history. But it by no means necessarily follows that the two kinds of description must always be in conflict, for anyone who describes a legal system must consider and compare both theory and experience. A true understanding of a legal system, as of chess or cricket, is only to be had from experience of the variety of action and result which can occur within the rules. The rules do not prescribe who will win, and (at least in a legal system) they are not always followed; but they do explain what the participants are up to.