Excerpted from the editorial version posted on http://www.constitution.org/tb/tb-1102.htm by permission of educational purposes.
The fairest and most rational method to interpret the will of the legislator, is by exploring his intentions at the time when the law was made, by signs the most natural and probable. And these signs are either the words, the context, the subject-matter, the effects and consequence, or the spirit and reason of the law. Let us take a short view of them all.
1. Words are generally to be understood in their usual and most known signification; not so much regarding the propriety of grammar, as their general and popular use. Thus the law mentioned by Puffendorf, which forbad a layman to lay hands on a priest, was adjudged to extend to him, who had hurt a priest with a weapon. Again; terms of art, or technical terms, must be taken according to the acceptation of the learned in each art, trade, and science. So in the act of settlement, where the crown of England is limited "to the princess Sophia, and the heirs of her body, being protestants," it becomes necessary to call in the assistance of lawyers, to ascertain the precise idea of the words "heirs of her body;" which in a legal sense comprize only certain of her lineal descendants.
2. If words happen to be still dubious, we may establish their meaning from the context; with which it may be of singular use to compare a word, or a sentence, whenever they are ambiguous, equivocal, or intricate. Thus the proeme, or preamble, is often called in to help the construction of an act of parliament. Of the same nature and use is the comparison of a law with other laws, that are made by the same legislator, that have some affinity with the subject, or that expressly relate to the same point.
Thus, when the law of England declares murder to be felony without benefit of clergy, we must resort to the same law of England to learn what the benefit of clergy is: and when the common law censures simoniacal contracts, it affords great light to the subject to consider what the canon law has adjudged to be simony.
3. As to the subject-matter, words are always to be understood as having a regard thereto; for that is always supposed to be in the eye of the legislator, and all his expressions directed to that end. Thus, when a law of our Edward III. forbids all ecclesiastical persons to purchase provisions at Rome, it might seem to prohibit the buying of grain and other victuals; but when we consider that the statute was made to repress the usurpations of the papal see, and that the nominations to benefices by the pope were called provisions, we shall see that the restraint is intended to be laid upon such provisions only.
4. As to the effects and consequence, the rule is, that where words bear either none, or a very absurd signification, if literally understood, we must a little deviate from the received sense of them. Therefore the Bolognian law, mentioned by Puffendorf, which enacted "that whoever drew blood in the streets should be punished with the utmost severity," was held after a long debate not to extend to the surgeon, who opened the vein of a person that fell down in the street with a fit.
5. But, lastly, the most universal and effectual way of discovering the true meaning of a law, when the words are dubious, is by considering the reason and spirit of it; or the cause which moved the legislator to enact it. For when this reason ceases, the law itself ought likewise to cease with it. An instance of this is given in a case put by Cicero, or whoever was the author of the treatise inscribed to Herennius. There was a law, that those who in a storm forsook the ship, should forfeit all property therein; and that the ship and lading should belong entirely to those who staid in it. In a dangerous tempest all the mariners forsook the ship, except only one sick passenger, who by reason of his disease was unable to get out and escape. By chance the ship came safe to port. The sick man kept possession, and claimed the benefit of the law. Now here all the learned agree, that the sick man is not within the reason of the law; for the reason of making it was, to give encouragement to such as should venture their lives to save the vessel: but this is a merit, which he could never pretend to, who neither staid in the ship upon that account, nor contributed any thing to its preservation.
 o Law of Nature and Nations 5. 12. 3.
 * It is an established rule of construction that statutes in pari materia, or upon the same subject, must be construed with a reference to each other; that is, that what is clear in one statute, shall be called in aid to explain what is obscure and ambiguous in another .... Thus the last qualification act to kill game (22 and 23 Car. 2. c. 25.) enacts, "that every person not having lands and tenements, or some other estate of inheritance, of the clear yearly value of 100l. or for life, or having lease or leases of ninety-nine years of the clear yearly value of 150l." (except certain persons) shall not be allowed to kill game. Upon this statute a doubt arose, whether the words or for life should be referred to the 100l. or to the 150l. per annum. The court of king's bench having looked into the former qualification acts, and having found that it was clear by the first qualification act (13 R. 1. st. 1. c 13 ) that a layman should have 40s. a year, and a priest 10l a year, and that by the 1 Ja. c. 27. the qualifications were clearly an estate of inheritance of 10l. a year, and an estate for life of 30l. a year they presumed that it still was the intention of the legislature to make the yearly value of an estate for life greater than that of an estate of inheritance, though the same proportions were not preserved; and thereupon decided, that clergymen, and all others possessed of a life estate only, must have 150l. a year to be qualified to kill game. Lowndes v. Lewis, E. T. 22 Geo. 3.
The same rule to discover the intention of a testator is applied to wills, viz. he whole of a will shall be taken under consideration, in order to decypher the meaning of an obscure passage in it. CHRISTIAN.
 11. So we must resort to the Common-Law of England to explain that part of the Constitution of the United States, which declares, that the benefit of the Writ of Habeas Corpus, shall not be suspended except in case of rebellion, or invasion.
 p l. 5. c. 12. §. 8.
 q l. 1. c. 11.
 12. On this subject of the interpretation of Laws in General, see Doctor Rutherforth's Inst. of Nat. Law, B. 2. c. 7.