One of my favorite ironies in the world of intellectual property involves the deadly magic of the word "invention." By simply using that word in describing the invention in a patent, you may cast a spell that sucks the life out of your intellectual property and destroys the value of your invention. How can such self-referential doom be possible? This is only possible thanks to the deep magic of certain highly-trained wizards dressed in the dark robes of judges, who have developed dark techniques for taking various statements about the "invention" to teleport new, unintended limitations into patent claims, making their scope smaller and smaller until they practically vanish into thin air.
Ronald Slusky in the Feb. 2010 issue of Intellectual Property Today has a good article, "Writing the Detailed Description, Part II," in which he discusses some of the problems in using the word "invention." It's not that the word itself is poison or a deadly potion, but statements about the "invention," if not carefully accompanied with detoxifying qualifiers, can be used to override the language of the claims and add poisonous, unintended limitations. For example, if you say, "Figure 1 depicts the invention," then there is a risk that details shown in the figure that may be completely optional or peripheral to the "real" invention may be assumed to be an integral part when a judge interprets your claims. If an accused infringer doesn't have those peripheral features, he may escape even if he appears to literally infringe the "plain meaning" of your claims.
You can still use the word "invention," but use it with caution, as in these examples: "In one embodiment of the invention, there may be . . ." or "Figure 1 shows a system that may be considered for use in some versions of the invention."
Some practitioners now strive to avoid using the word "invention" at all, but perhaps that is unnecessarily restrictive.
Slusky urges practitioners to understand the invention thoroughly before writing the Summary or Detailed Description to avoid making sloppy statements about what the invention is or is not, in order to ensure that the specification really does justice to the claims. For inventors, make sure you are working a patent attorney or agent patient enough to learn from you and really understand what your invention is and what its points of novelty and nonobviousness are relative to the prior art. Make sure that the way she or he wants to describe your patent adequately reflects your real invention. It's the up-front work between you and your patent practitioner that will determine the value of the writing in the patent and the ability of your future patent to provide value.
In the drafting of the patent, make sure this simple commandment is obeyed: "Know thy Invention!" And then speak its name with reverence and caution, or you may cast a spell to aid your adversary.