Recently in Secure Web Conference Corp. v. Microsoft, __Fed App’x __ (Fed. Cir. 2016)(Stoll, J.), the panel explained its decision in terms of the “essence of the invention”.
Attached is an excerpt from FIRST TO FILE PATENT DRAFTING, § 8[d],“Essence” of the Invention (pp. 189-93), that explains the origins of the quoted terminology and why it is a nineteenth century anachronism.