Many examiners will raise issues with claims that include a term of approximation, like “substantially.” While one may elect to shorten prosecution and simply remove the term in some instances, there can be situations where it is critical to retain some flexibility in the claim scope so as to avoid easy design around options.

MPEP §2173.05(b) specifically addresses this issue and can provide helpful support for applicants wanting to retain some flexibility in claim scope. The MPEP explains in Section III how approximation terms are to be reviewed, and specifically addresses “substantially”:

The term "substantially" is often used in conjunction with another term to describe a particular characteristic of the claimed invention. It is a broad term. In re Nehrenberg, 280 F.2d 161, 126 USPQ 383 (CCPA 1960). The court held that the limitation "to substantially increase the efficiency of the compound as a copper extractant" was definite in view of the general guidelines contained in the specification. In re Mattison, 509 F.2d 563, 184 USPQ 484 (CCPA 1975). The court held that the limitation "which produces substantially equal E and H plane illumination patterns" was definite because one of ordinary skill in the art would know what was meant by "substantially equal." Andrew Corp. v. Gabriel Electronics, 847 F.2d 819, 6 USPQ2d 2010 (Fed. Cir. 1988).

If the specification provides some guidelines, there is generally a good basis to push back against a rejection of the term as indefinite. However, one does not always have explicit language in the specification giving guidelines. Nevertheless, examiner often confuse relative terms with terms of approximation, and the applicant can take advantage of this confusion. A recent example is Appeal 2022-003253 Application 14/904,176. Here, the examiner based the rejection on an assertion that the term was relative. The PTAB explained that this was improper, without resorting to the specification to even look for guidelines because the rejection never got that far (some internal citations omitted):

It is well settled that words of approximation, such as “generally” and “substantially,” are descriptive terms commonly used in patent claims to avoid a strict numerical boundary to the specified parameter. The term “substantial” is often used as a modifier to imply “approximate” rather than “perfect.” Here, the Examiner errs by treating the term “substantially” as a term of degree rather than a term of approximation. The definiteness of a term of degree involves comparison to a baseline. See Liberty Ammunition, Inc. v. United States, 835 F.3d 1388, 1395 (Fed. Cir. 2016). In Liberty Ammo, the term of degree at issue was “reduced area of contact,” which entailed comparing an “area of contact” that was “reduced” relative to a baseline area of contact. Id. at 1395-96. The definiteness principle regarding a term of degree does not apply to the term of approximation “substantially” as used in this case. Anchor Wall, 340 F.3d at 1311.

So, know the rules and think strategically about whether and how to use approximate terms like substantially. Enjoy the Holidays!