This is a remarkable opinion. I will simply reproduce the relevant passages. Be sure to read through to the third paragraph. This one is going to be in a lot of casebooks:
It is helpful to note at the outset that the interpretation of statutes comes in three flavors. The first and most conventional is the extraction of the original meaning of the statute—the meaning intended by the legislators—and corresponds to interpretation in ordinary discourse. Knowing English I can usually determine swiftly and straightforwardly the meaning of a statement, oral or written, made to me in English (not always, because the statement may be garbled, grammatically intricate or inaccurate, obtuse, or complex beyond my ability to understand).
The second form of interpretation, illustrated by the commonplace local ordinance which commands “no vehicles in the park,” is interpretation by unexpressed intent, whereby we understand that although an ambulance is a vehicle, the ordinance was not intended to include ambulances among the “vehicles” forbidden to enter the park. This mode of interpretation received its definitive statement in Blackstone’s analysis of the medieval law of Bologna which stated that “whoever drew blood in the streets should be punished with the utmost severity.” William Blackstone, Commentaries on the Laws of England *60 (1765). Blackstone asked whether the law should have been interpreted to make punishable a surgeon “who opened the vein of a person that fell down in the street with a fit.” (Bleeding a sick or injured person was a common form of medical treatment in those days.) Blackstone thought not, remarking that as to “the effects and consequence, or the spirit and reason of the law … the rule is, where words bear either none, or a very absurd signification, if literally understood, we must a little deviate from the received sense of them.” Id. *59–60. The law didn’t mention surgeons, but Blackstone thought it obvious that the legislators, who must have known something about the medical activities of surgeons, had not intended the law to apply to them. And so it is with ambulances in parks that prohibit vehicles.
Finally and most controversially, interpretation can mean giving a fresh meaning to a statement (which can be a statement found in a constitutional or statutory text)—a meaning that infuses the statement with vitality and significance today. An example of this last form of interpretation—the form that in my mind is most clearly applicable to the present case—is the Sherman Antitrust Act, enacted in 1890, long before there was a sophisticated understanding of the economics of monopoly and competition. Times have changed; and for more than thirty years the Act has been interpreted in conformity to the modern, not the nineteenth century, understanding of the relevant economics. The Act has thus been updated by, or in the name of, judicial interpretation—the form of interpretation that consists of making old law satisfy modern needs and understandings. And a common form of interpretation it is, despite its flouting “original meaning.” Statutes and constitutional provisions frequently are interpreted on the basis of present need and present understanding rather than original meaning— constitutional provisions even more frequently, because most of them are older than most statutes.