Equity is the soul and spirit of the law

Institutes of American Law by John Bouvier (1882)

Volume 2. Fifth Book. Of Equity. Chapter One - The Nature and Principles of Equity. 

3724. The nature of equity:

"There is a kind of equity which is founded in natural justice, in honest and right, and which arises ex aequo et bono; this is called natural equity. It corresponds precisely with the definition of justice or natural law, which is a constant and perpetual will to give to every man what is his. This kind of equity embraces so wide a range that human tribunals have never attempted to enforce it. Every code of laws has lfet many matters of natural justice or equity wholly unprovided for, from the difficulty of framing general rules to apply to them, from the almost impossibility of enforcing a compliance with its requirements, and from the doubtful nature of the policy of attempting to give a legal sanction to duties of imperfect obligation, such as charity, gratitude, or kidness. Differing altogether from this, there is another kind, called civil equity. This is deduced from and governed by such civil maxims as are adopted by any particular state or community. This alone will form the subject of this book." 

"Civil equity may be taken in two senses in jurisprudence. It is, in the first place, that rule of right which determines the decisions of a judge, when he has to follow the strict rule to which he is obliged to conform by the requirements of the law; and, secondly, which is its true technical meaning, it is justice exercised not according to the rigor of the law, but softened and moderated so as to attain the views of the legislator; it is to correct the law when it is defective by reason of its universality." 

"Law is nothing without equity, and equity is everything, even without Law. Those who perceive what is just and what is unjust only through the eyes of the law, never see it as well as those who behold it with the eyes of equity. Law may be looked upon, in some manner, as an assistance for those who have a weak perception of right and wrong, in the same way that optical glasses, are useful for those who are shortsighted, or those whose visual organs are deficient. Equity, in its true and genuine meaning, is the soul and spirit of the law; positive law is construed and rational law is made by it."

"When in certain cases the law is clear, it would be doing iniquity to depart from it under the pretext of tempering and modifying its dispositions by particular principles of greater equity; otherwise, the law, established to give to all men an invariable rule for their conduct, would have nothing certain, and the citizens would in vain attempt to repose under the shadow of its dispositions." 

"Equity is not arbitrary opinion of the judge; it is subject to certain and fixed rules; for, unless it be directed by science, it becomes uncertain and unknown, and in such case the magistrate must tremble while sitting in the temple of justice. His mind will wanter in pursuit of a phantom of equity purely imaginary. Frequently, what appears just to a man seems unjust to another, and yet both act in good faith; each sustains the side he has adopted apparently with arms of equal power, which renders it extremely difficult to decide to whom the victory should be awarded. But equity, like truth, is but a unit; it must manifest itself by its own power, and it is never better seen than through the medium of the law. There it is made manifest, and it may be adopted without fear of a mistake, because the law must be considered as the wisdom and foresight of the legislator, and he is presumed to have studied equity and embodied it in his work."