The origins of the English patent system lie in the Crown’s prerogative to grant monopolies. Letters Patent issued under the Great Seal were a command from the sovereign that had the power of law and had to be respected by all subjects in the realm.[4] The increasing grant of trading monopolies by James I as a means of rewarding his political supporters led to pressure for the practice to be restricted.[5] This ultimately led to the passage of the Statute of Monopolies in 1624,[6] which declared all monopolies to be void with the exception of monopolies for 14 years for “any manner of new manufacture … [granted] to the true and first inventor…” [7]

Traditionally, the scope of protection provided by an English patent was determined by the common law. This was based on the wording of the grant of Letters Patent itself with its royal command that others “do not directly or indirectly make use of or put into practice the said invention, nor in anywise imitate the same.”[8] During the reign of Queen Anne, the law officers of the Crown began to require as a condition of grant that “the patentee must by an instrument in writing describe and ascertain the nature of the invention and the manner in which it is to be performed.”[9]  From 1734, the requirement to file a “specification”, as this document became known, became standard for the grant of all patents.[10]

At this time, the concept of a “claim” acting to define a patentee’s monopoly was unknown. Patent litigation in this period was typified by novelty actions, testing whether any essential part of the patent had been disclosed to the public before, and enablement actions, in which juries were asked to determine whether the specification described the invention well enough to allow members of the appropriate trade to reproduce it.[11]  In both cases it was the specification rather than any “claims” which determined whether or not the patent would survive.

Given these antecedents, it is not surprising that the earliest patent acts [12] passed by the U.S. Congress do not include any reference to “claims.” Rather, following English precedents, an inventor was required to file  “a specification … containing a description of the thing ... by him … invented … which specification shall be so particular … as not only to distinguish the invention or discovery from other things before known and used, but also to enable a workman … to make, construct or use the same…” [13]

Gradually a practice developed both in the U.K. and in the U.S. of including sentences in a patent pointing out the novel features claimed. In 1822, in Evans v. Eaton [14] the U.S. Supreme Court held that the “distinguish” language of the 1793 Patent Act required both that a patent sufficiently described an invention “so as to enable artisans to make and use it …[and] to put the public in possession of what the party claims as his own invention.” In 1836, Congress undertook a major revision of U.S. patent law, which in addition to creating the U.S. Patent Office and setting up a system of examination against the prior art, also adopted the rule of Evans v. Eaton by requiring that the inventor in a specification “particularly specify and point out the part, improvement or combination which he claims as his own invention or discovery.” [15]

Developments in the U.K. mirrored those in the U.S. By the early nineteenth century it was appreciated that the specification served a dual function, first describing an invention so as to enable the invention to be put into practice, and second, defining the scope of the granted monopoly. It was also appreciated that the detailed description necessary to fulfil the first purpose was not particularly suited to the second. Hence in an effort to obtain broader protection, patent applicants began adding “claims” to the specification. The inclusion of claims became obligatory in the U.K. in 1883 with the passage of the Patents, Designs and Trade Marks Act, which required a patent to include “a distinct statement of the invention claimed.” [16]

With the mandatory inclusion of claims in the U.S. and the U.K., judicial attitudes began to change. Whereas initially claims were considered to be merely guides to identifying what an inventor considered to be his invention, [17] from the 1850s U.S. judges increasingly began to express the view that in seeking to ascertain the invention “claimed” in a patent the courts should limit their enquiries to interpreting the summary, or “claim.” [18] Similarly in the U.K. the words of the claims came to be treated as “fence posts” defining the limit of protection [19] as reflected in Lord Russell’s dictum in EMI v. Lissen [20]  that: “What is not claimed is disclaimed… A patentee who describes an invention in the body of a specification obtains no monopoly unless it is claimed in the claims.”

Even so, the courts still accepted that the protection conferred by a patent was not completely limited by the wording of the claims. In the U.K. a strict literalist approach was supplemented by the doctrine of the “pith and marrow” by which a defendant could still infringe a claim if he took the essential integers of an invention, even if other inessential features were omitted or substituted with mechanical equivalents. [21] In the U.K., claim construction therefore became a two-stage process by which, after the literal scope of a patent claim had been interpreted, restrictions present in the literal wording of a claim could be ignored if they were inessential. [22] The court’s inquiry was, however, limited to determining the essential elements or integers and did not range so far as the question of whether an infringer had used the essence of an invention itself. [23] Similarly in the U.S., it remained possible to infringe a patent even where there was no literal infringement if there was “equivalence” between elements of the accused product or process and the claimed elements of the patented invention. [24]