Invention represents a form of knowledge that is usually identified with its readable textual description. An invention is seen as a described invention.
At the opposite end of the spectrum are embodied inventions: described inventions that have been applied in a specific, material, case. Formidable questions arise here like: ``what inventions are embodied in an Airbus A 380?'' or ``Are any inventions embodied in the human body?''.
Patenting is about the creation of a body of described inventions and its use, whereas infringement deals with the matching between described inventions and embodied inventions. The state of the art contains described inventions as well as embodied inventions though the degree to which is a matter of dispute and development. By default we will use the term ``invention'' to denote a described invention. If an embodied invention is meant this will always be made explicit, or be clear from the context.
Following the EPT we will explicitly not insist on the requirement that an invention be new.3An invention has been new at the time of its making, later on it is still an invention though not new anymore.
The advantage of this terminology is that a patent application can be said to contain an invention even if its novelty is contested. It is very much like mathematical theorems: scientific journals prefer new theorems, but the concept of a theorem as such in no way refers to novelty. Similarly, the discovery of radio-activity is still to be classified as a discovery, though not a new or recent discovery.
We do not assume that all inventions constitute patentable subject matter by definition. Thus some inventions may escape patenting, for instance, if regulations have been adapted because the economic or legal effects of patenting certain classes of inventions are considered detrimental.
Summing up: being an invention is independent of either specific patents or even the existence or operation of entire patenting systems, like being a work is independent of the existence of copyright regulations. Moreover, inventions go through a life-cycle, but never cease to exist.
It is the embodiments that may cease to exist, and in some cases all descriptions of an invention may disappear. From a theoretical point of view the questions ``Was the invention of the combustion engine done by Archimedes '', and ``Was the invention of the combustion engine known to the ancient Greeks'' are reasonable historic questions, currently both provided by a negative answer. Such questions are never seriously asked, but do not differ in principle from the reasonable question ``Was RSA known to the KGB before R, S and A developed it?'' [9].