Patent Claim identifies the field of the invention. The preamble of an independent claim can summarize the type of invention, identify the relationship between the invention and the prior art, describe how the invention operates upon some external article, and define the purpose of the invention.
The preamble should be realistically narrow in scope. For example, for an invention in a bicycle, a preamble that says “vehicle” would appear to be of broader scope than a preamble that says “bicycle.” Yet, if the invention is clearly directed to a bicycle, there is no benefit to having a preamble say “vehicle,” which is more encompassing than the invention itself.
Conversely, if the preamble says “bicycle,” but the invention is adaptable not only for bicycles but for motorcycles, and if an infringer were later to market a product which had all of the feature limitations in the claim, but which was a motorcycle rather than a bicycle, the infringer might argue that the claim does not reach the accused product because the claim is limited in scope to a bicycle. Therefore, the preamble must be sufficiently broad to cover the product in the preferred embodiment to which the inventor has directed his attention (bicycle), but also to cover other embodiments, such as “two-wheeled vehicles,” to which the invention may be directed.
To avoid a too-limited-scope preamble, the claim writer might be tempted to merely recite the broad “Apparatus comprising” or use “device” or a similar non-specific noun. But a too broad preamble is also not good practice, although not improper.
One good practice is that the title in the specification and the preamble of the claims should be correlated and consistent. If one is changed, the claim writer should consider changing the other. A preamble limited to the title of the invention as it appears should always be enough. A good preamble is short. It does not tell a story. It does not typically describe the ultimate purpose of the invention.
On the other hand, in some cases, the preamble may have to be longer because in order to understand an invention, one must understand its context. Therefore, sometimes the purpose of the invention is recited in the preamble before the transition word, as in “Apparatus for cooling an engine, the apparatus comprising.. .”
The preamble of the dependent claims need not be as lengthy as the preamble of the independent claim. Often, the preamble of the dependent claim merely consists of the major noun of the preamble of the independent claim. The preamble of the dependent claim must be consistent with that of the claim from which it depends. In the above example, the dependent claim preamble may simply be “The apparatus of claim… .”