The initial patentability analysis focused on the teachings of the references, and a comparison was made to discern if there
was a patentable difference between your invention and previous ones. The focus now is to determine the existence of any fundamental
blocking patent that might prevent you from commercializing your invention. It is the "claims," rather than the teachings
of each patent, that must now be analyzed.
Claims are numbered statements located at the end of a patent that define the legal scope of coverage to a patentee. A product
may infringe these claims through literal infringement or under the judicially created doctrine of equivalents (discussed
in more detail later). The analysis begins with a determination of what is claimed by the prospective patent; this is followed
by a determination of whether what is claimed by this patent has been made, used, or sold by another. Claims are similar to
the metes and bounds of a property deed, and they define the right that a patent confers on the patentee to exclude others
from making, using, or selling the protected invention. Claims are read by giving the words of the claim their ordinary meaning,
and if doubt exists as to the meaning of one or more words, reference is made to the specification and file wrapper (i.e.,
prosecution history) for guidance. Moreover, even in those circumstances in which the claim language is free from ambiguity,
all parts of the patent, i.e., the specification, the drawings, and the file wrapper, must be considered in the interpretation
of the claims.
Literal infringement is found when, in at least one claim of an issued patent, each and every element of that claim is "literally"
met by the accused product or process in a one-to-one correspondence. Even if the accused product or process incorporates
additional elements that may be patentable, literal infringement may be alleged by the patentee. Literal infringement often
is found when the accused product is an improvement of a previously existing product. Let's go back to the original Bayer
Aspirin® patent. For purposes of this article, we shall assume that the first claim stated that it covered acetylsalicylic acid (note
that the claim doesn't state that exactly, and it adds other limitations that will be ignored for purposes of this article).
For the sake of discussing infringement issues, we shall also assume that the patent is still in effect, for it is impossible
to infringe a patent that has expired (as has the original Bayer Aspirin® patent). Therefore, for our purposes, the only difference between the original patented product and your new product is the
substitution of a methyl group for hydrogen. This seemingly simple change is sufficient, under the fact pattern used here,
to prevent literal infringement from being proven. However, this merely is the first step in a longer process.
Doctrine of Equivalents Infringement
A patent claim that is not literally infringed may still be infringed via a judicially created mechanism known as the doctrine
of equivalents. The doctrine traces its origins to a US Supreme Court opinion enunciated in the case of Graver Tank.2 It may be invoked by a patentee against the producer of a later device if the later device performs substantially the same
function in substantially the same way, to obtain the same result. This is known as the tripartite or three-pronged test.
Failure to establish any one of the prongs of equivalence precludes a finding that an accused product is the equivalent of
the claimed device.
While the doctrine of equivalents extends the claims beyond their literal words, it does not prevent the manufacture, use,
or sale by others of every device generally similar to the patented invention. Any practitioner wishing to precisely explore
where the outer boundaries of this doctrine lie is encouraged to consult the en banc opinion rendered by the Court of Appeals for the Federal Circuit in Festo 3 as modified by the US Supreme Court in its Festo 4 decision in light of its previous opinion in Hilton-Davis 5 (advancing an "insubstantial differences" test), as well as the remanded Festo decision by the Court of Appeals, Federal