While it may seem crazy to those outside of patent law, the scope of a claimed invention can be completely different depending on whether the invention “comprises” certain elements, or “consists of” those elements. The former is open-ended, meaning if the accused infringer uses the claimed elements, but adds more features, there is still infringement. In contrast, the latter is a closed group such that when the accused infringer uses extra features, there is no infringement. Of course there are nuances, but the general rule is quite stark.

In patent prosecution, these distinctions also are critical for evaluating patentability. If the prior art cited by an examiner has extra elements and the claim has closed language like “consisting of,” then the prior art does not anticipate the claimed invention. In contrast, if the open-ended language is used, then the additional elements in the cited reference do not preclude a finding of anticipation. See MPEP 2111.03, for example.

Where things get messy is when the claims start to combine open and closed transitional phrases. There is nothing logically incorrect in using a combination of closed and open-ended constructs to lay out a claim. Consider an example of the form:

A system, comprising:

(a) component 1; and

(b) component 2 coupled to component 1, wherein component 2 consists of metal.

As a shorthand - the claim essentially covers a system that has at least component 1 and component 2 coupled together, but only if component 2 is metal with no other materials. Additional components may or may not be included, without changing the result. However, if component 2 includes plastic and metal, it is outside the scope of the claim.

A real-life example of a claim that used both closed and open-ended language was considered by the Federal Circuit in Dippin’ Dots, Inc., v Mosey, 476 F.3d 1337 (Fed. Cir. 2007). The case involved Dippin’ Dots, Inc.’s (DDI’s) patent for a method of preparing and storing a free-flowing, frozen alimentary dairy product. Claim 1 was a method claim that used the transition “comprising” and then listed out six method steps. One of those steps required freezing the dripping alimentary composition into beads, and then later steps addressed operations on those beads. The alleged infringer used a multitude of shapes and thus argued that the claim was limited to forming beads. The Federal Circuit addressed this issued directly in the context of the “comprising” language of claim 1:

[…]As to DDI’s second argument, we acknowledge that the term “comprising” raises a presumption that the list of elements is nonexclusive. See Genentech (Fed. Cir. 1997). However, “‘[c]omprising’ is not a weasel word with which to abrogate claim limitations.” Spectrum (Fed. Cir. 1998). “Comprising” appears at the beginning of the claim—“comprising the steps of”—and indicates here that an infringing process could practice other steps in addition to the ones mentioned. Those six enumerated steps must, however, all be practiced as recited in the claim for a process to infringe. The presumption raised by the term “comprising” does not reach into each of the six steps to render every word and phrase therein open-ended[…].

Thus, while a system claim might be open-ended, and thus could include additional components beyond those listed, this open-endedness does not extend to undo explicit limitations that come later.

But of course things can get even more complicated. What if someone adds yet another layer: open - closed - open? Is that even possible? Well Delta Airlines showed that there is nothing wrong with such an approach in a recent PTAB decision (sn 14/966,988). Here are the relevant terms of claim 1 (emphasis added):

1. A computer-implemented method for facilitating the execution of a path of air travel, said method comprising the steps of:
receiving … hazard data indicative of a deterministic intensity of at least two hazards of at least two hazard types …;
converting …the deterministic intensity of each of the at least two hazards indicated by the hazard data to fit an atmospheric state intensity scale, the atmospheric state intensity scale consisting of and being defined by a plurality of deterministic intensity values that are each common across each of a plurality of hazard types…

Here, the examiner asserted that the “consisting essentially of” language did not limit the “comprising” language of the preamble because the “plurality” feature is open-ended itself. Delta argued that the pertinent phrase in the claim language is “an atmospheric state intensity scale consisting of and being defined by a plurality of deterministic intensity values that are each common across each of a plurality of hazard types.” In this context, Delta explained that it was evident that, despite the limit of the “plurality of deterministic intensity values” not being closed-ended, however many values are present must all (due to the closed-ended consisting of language) be common across each of the provided hazard types. The PTAB agreed with Delta.

Nevertheless, Applicants should be careful not to implicitly “undue” transitional phrase meanings with later claim elements. Here, the claim elements held together logically and were consistent with the specification in a way that enabled using open, then closed, and then open again, terms. The meanings discussed above are presumptions - meaning the applicant can undo them. As such, when combining open and closed-ended transitions in the same claim, be careful that everything holds together and do not let an examiner simply ignore one or the other to suit an improper rejection.