The basis for claim drafting is found in the statute, namely 35 USC section 112. This section of the statute states that the specification shall conclude with one or more claims particularly pointing out and distinctly claiming the subject matter for which the applicant regards as his invention.
However, various rules and practices have developed in order to fulfill the mandate of particularly pointing out and distinctly claiming the subject matter. In general, this means that the claims must define the invention which means the claimed subject matter. Thus, there must be sufficient detail that the patent examiner and subsequently the world of perspective infringers can understand what the claimed subject matter is.
A first rule is that omnibus or formal claims are not permitted in utility patents. For example claims which recite 'my invention substantially as shown and described' or 'any and all features of novelty described' are not permitted in the United States. These types of claims if allowed, would allow too much uncertainty as to the patent coverage. The inventor must define the patent coverage as precisely as circumstances permit.
The reason for demanding certainty in patent coverage is that the world of potential infringers should have a clear understanding of the patent coverage. If uncertainty were permitted in patent coverage, the world of potential infringers would have to guess the extent of the patent coverage that is covered by a particular patent. This is the basis for the duty to define the area to be covered by the patent claims as precisely as circumstances permit.
An analogy can be made with the description of the boundaries for a plot of land. The patent claim drafter must stakeout the precise boundaries of the claim in a manner that is similar to the description for the boundaries for a plot of land.
This concept is extremely useful for the potential infringers but may disadvantage the patentee because the true extent of the usefulness of the patent may not be evident until years in the future. The true extent may extend beyond the description found in the current specification and may not be captured by the literal boundaries that the patentee has set forth in his claims. This conflict is inherent between the potential infringers and the patentee.
Another statue which affects the permitted claim language is 35 USC section 101 which sets out four main categories or pigeonholes of technical subject matter for which utility patents can be granted. The statutory classes are process, machine, manufacture or composition of matter.
Such things as mathematical formulas, bookkeeping systems and articles formed in nature have been held to be unpatentable because they are not found to be within the classes set up by Congress.
A claim regardless how artfully drafted must define the invention in such a way that it fits into one of the statutory classes. A failure to fit into the statutory class may result in a failure of the claim to be patentable.
Ornamental designs and certain agricultural plants are separate statutory classes with different rules.
This does not mean that these things cannot be part of a patent application. These things can be combined with the permitted statutory classes. For example, a device could be controlled by a computer which executes a mathematical formula. The mathematical formula per se cannot be claimed as the patentee's invention. However, the device which operates in accordance with the mathematical formula can be a proper object for claimed subject matter.