In any field of legal study, there are certain terms which, while not corresponding to distinct fundamental concepts, come to acquire currency as regular symbols or building-blocks in legal argument, either through their inclusion in some key text, or through being recognised as convenient encapsulation of a bundle of concepts or conditions. The generally well-recognised danger in the use of such symbolic notation is that the term in question may come to be used with insufficient regard to the nucleus of ideas which existed before it was affixed as a label, and the manipulation of which it was merely intended to facilitate. Furthermore, what may be called the “common” meaning of the term in question – the meaning it has in a non-legal or non-specialist dictionary – may exercise a surreptitious influence, causing the legal meaning of the term to drift in a manner unjustified by legal considerations. For these reasons, such terms need to be scrutinised from time to time in the light of their origin and background, in order that such drifts may be detected, and the danger avoided of legal exactitude being prejudiced by linguistic convenience.