In the United States, Judge Learned Hand has described its purpose as being "to temper unsparing logic and prevent an infringer from stealing the benefit of the invention.
On 21 March 2013, the Federal Patent Court of Switzerland adopted an approach similar to the three-prong test applied in Germany.
A person skilled in the art would not consider the organic catalyst TEMPO as a solution of equal value to the ruthenium salts specified in claim 1.
The court set forth that the replacement of the claimed p-Toluenesulfonic acid with pyridine/water constituted basic knowledge taught during the first years of an undergraduate course in organic chemistry.
Their Lordships took the view that if the patentees had deliberately framed their claim in such way as to exclude the alleged infringing act, then they should be held to the wording they had chosen.
"[7] The much stricter approach to claim construction became open to review after 1977, when the UK joined the European Patent Convention (EPC).
[8] In Catnic Components Ltd v Hill & Smith Ltd (1982) the House of Lords swept away all of the earlier case law on "mechanical equivalents” and "pith and marrow", and held that a patent specification should be given a “purposive construction” rather than a purely literal one.
The question to be asked should be whether a skilled person reading the patent would understand that strict compliance with a word or phrase within the claim was intended by the patentee to be an essential requirement, even if it could have no material effect upon the way the invention worked.
[9] The specific questions used by the courts to achieve the required “purposive construction” settled into stable form with Improver v Remington (1990) and the House of Lords decision in Kirin-Amgen (2004).
[15] Also, based on the public dedication principle, a patentee may not invoke the doctrine of equivalents to recapture subject matter disclosed but not claimed in a patent.