Being your own lexicographer means is that you who can define your invention using whatever terms you choose, and after attributing pretty much whatever meaning you want to give to the terms you use. Indeed you get to define the terms you use so long as any special meaning you assign to any particular term is clearly set forth in the specification (i.e., the written text of the application other than the patent claims). In essence, you can define terms in the specification so that you can then later in the patent claims use the term. If you do define the term in the specification the meaning attributed to that term would trump any other possible definitions when it comes time to interpret the claims.
Taking this “be your own lexicographer” rule to the extreme, a patent applicant may even use terms in a manner contrary to or inconsistent with one or more of their ordinary meanings as long as the description provided in the specification clearly and unambiguously redefines the terms. See, e.g., Process Control Corp. v. HydReclaim Corp., 190 F.3d 1350, 1357, 52 USPQ2d 1029, 1033 (Fed. Cir. 1999) (“While we have held many times that a patentee can act as his own lexicographer to specifically define terms of a claim contrary to their ordinary meaning,” in such a situation the written description must clearly redefine a claim term “so as to put a reasonable competitor or one reasonably skilled in the art on notice that the patentee intended to so redefine that claim term.”) Notwithstanding, when acting as your own lexicographer, redefining terms to have contrary meanings is exceptionally dangerous and should be avoided at all costs. Not only is it poor drafting practice, but keeping contrary meanings consistently straight without deviation is not easy. There are many things that are critically important when drafting a patent application, but consistency is at the very top of the list. So even though you could get creative with your definitions that is not something to at all be encouraged.
Knowing that you can define the terms you use to disclose your invention is interesting, but it begs an important question. Why would you want to define terms in the specification instead of defining them in the claims?
As a general rule, you want to keep the claims as short and sweet as possible. Too many words and qualifications in a patent claim will make things unwieldy and cumbersome, not to mention very difficult to work with given the picky format requirements the Patent Office imposes. Therefore, it is much easier to define terms in the specification and then just use the term in the claim.
For example, the concept of “capturing the king” in a game of chess is quite complicated, at least if you are going to try and define all the possible ways that a king can be “captured.” Think of all the different ways the pieces can move. The bishop can move multiple spaces at a diagonal, the rook can move multiple spaces in a straight line, the knight moves in a “L” pattern, the queen can more multiple spaces either diagonally or straight, and a pawn can move only forward one, or sometimes two, spaces at time but can only capture a piece moving diagonally forward one space. If you were going to write a claim for playing chess, which would include declaring a winner, you would be much better off defining what it means to “capture the king” in the specification and then leverage that definition in the claims.
Ideally, the specification should serve as a glossary to the claim terms so that those who will read the patent, such as the patent examiner for example, can clearly ascertain the meaning of the claim terms. It is also greatly preferable to make sure that the terms are given the meaning that you want them to have rather than the meaning that may be attributed to them later. It is true that the ordinary plain meaning of the terms as would be understood by one of skill in the relevant technology field will be applied if you do not provide your own definitions, but leaving nothing to chance is generally a good idea. It is an absolute prerequisite if you are using a term that has multiple possible meanings, or if you are referring only to a certain subset of what the term generally means or could mean.
When drafting the specification it is also important to keep in mind that correspondence between the specification and claims is required by 37 CFR 1.75(d)(1), which provides that claim terms must find clear support in the specification so that the meaning of the terms may be ascertainable by reference to the specification. When you peel back the legalese this requirement is not difficult to understand. You absolutely must disclose your invention in the specification in order to be able to claim it as your own.
As you may be aware, patent claims define the exclusive rights granted to the patent owner. But you cannot claim what you have not disclosed in the specification. Therefore, it is essential to make sure that you describe your invention to the fullest extent possible in the specification. Conceptually, that means describing the invention in a variety of different ways – (1) broadly and generically; (2) with extreme specificity; and (3) all the variations (i.e., combinations and permutations) in between the most broad articulation of the invention and that version described with extreme specificity. For more information on completely describing your invention please see:
Many inventors mistakenly believe they want to describe their invention only broadly, but that is a huge mistake. If you leave out the details you cannot later add them to the application, and if they are not in the application they cannot be used in the claims. YOU CAN ADD CLAIMS AFTER YOU FILE AN APPLICATION.
I shout that purposefully because so many inventors are unfamiliar with this basic truth. You cannot, however, add new matter. The difference is this: You cannot add any description or detail to a non-provisional utility patent application after it has been filed because that would be considered new matter, however you can add new patent claims that are supported by the original disclosure of the invention that arrived at the time you filed the patent application. Therefore, it is essential to include a broad, general description, as well as ever more narrow and specific descriptions of the invention and the elements that make up the invention.
So the moral of the story is this: Go forth and be your own lexicographer, describe your invention fully, but stay away from contrary meanings.