This method was borrowed by the early English chancellors from the canon law, and their reasons for borrowing it were much the same as those which caused its original adoption by the canonists. The canon-law courts had power only over the souls of litigants; they could not touch their bodies nor their property. In short, their power was spiritual, not physical, and hence the only way in which they could enforce their sentences was by putting them into the shape of commands to the persons against whom they were pronounced, and inflicting upon the latter the punishments of the church (ending with excommunication) in case of disobedience. If these punishments proved insufficient to secure obedience, the civil power (in England) came to the aid of the spiritual power, a writ issued out of chancery (de excommunicato capiendo), and the defendant was arrested and imprisoned.
When the English chancellor began to assume jurisdiction in equity he found himself in a situation very similar to that of the spiritual courts. As their power was entirely spiritual, so his was entirely physical. Through his physical power he could imprison men’s bodies and control the possession of their property; but neither his orders and decrees, nor any acts as such done in pursuance of them, had any legal effect or operation; and hence he could not affect the title to property, except through the acts of its owners. Moreover, his physical power over property had no perceptible influence upon his method of giving relief. Even when he made a decree for changing the possession of property, it took the shape, as we have seen, of a command to the defendant in possession to deliver possession to the plaintiff; and it was only as a last resort that the chancellor issued a writ to his executive officer, commanding him to dispossess the defendant and put the plaintiff in possession.
Such, then, being the two methods of giving relief, it is easy to understand why that of equity has supplemented that of the common law; for the former is strong at the very points where the latter is weak.
It has been said that the extent of the jurisdiction exercised by equity over common-law rights is measured by the requirements of justice. But what are the requirements of justice? In order to answer that question we must first know definitely in what particulars the common law fails to give to common-law rights all the protection which it is possible to give, and which, therefore, ought