The proximate cause, whether an event covered by a policy (“peril”) or an event excluded from a policy (“exception”), “is the dominant or effective or operative cause.” So says MacGillivray and Parkington.1 So say the courts. It is hard to disagree. It is also hard to understand what it means and hence hard to apply it. The result is that most judges are reluctant to commit themselves to greater precision and that those lawyers who press further, judges or writers, do not agree.

The decision in American Cyanamid Co. v. Ethicon Ltd. was hailed. rather unenthusiastically, as a revolutionary development in the law governing interlocutory injunctions; it was seen as an abandonment of the earlier approach exemplified by, although not discussed in, Stratford and Sons Ltd. v. Lindley. There was some indignation at the apparent loss of a quick, relatively cheap means of settling cases by decision on an application for an interlocutory injunction, and considerable doubt as to the suitability of the principles set out by Lord Diplock in Cyanamid for use in all types of interlocutory action.

The common law doctrines relating to mixtures and improvements of personal chattels give the impression, to most English lawyers, of being somewhat mysterious. Proprietary interests come and go like ships in the night, now mingled with rights to possession, now quite separate. But although cases involving proprietary claims are not common, the issue often arises as to A's personal rights against B, where B has without A's consent expended effort on A's property, and B's personal rights against A (if any) in respect of the improvement.