delivered the opinion of the court.'
This appeal is from the decision' of the Patent Office Board of Appeals, Which affirmed the rejection of claims 1-9, lo'ánd 17 in-appellants’ application serial No’. ’ .392,635, filed Augiist 27,/1964, for “Polymeric Material and Process of Preparing the "Same.” . .
The invention is a new and unobvious class of polyimidés pseful in making molded articles and also useful as 'coatings or self-sirpp'oi’ting films. Claim 1 is illustrative for framing the issues before us:
1. A polyimide of (1) a diamine, (2) 3,4-dicarboxy-l,2,3,4-tetrahydro-l-naplithalenesuccinic dianbydride and (3) a different dianbydride of an organic tetracarboxylic acid, wherein the mol percent ratio of (2) : (3) is between about 35: 65 and 65 : 35, respectively.
The rejection is solely for insufficient disclosure, the examiner having-stated that the recitations “a diamine’ and ‘a different dianhydride of an organic tetracarboxylic acid’ are considered to be too broad to be supported by the disclosure.” The board agreed.
It has not been contended by the Patent Office that the disclosure fails to enable -a person skilled in the art to make and -use the entire class of polyimides claimed. The sole issue is whether the specifications satisfies the description requirement of the first paragraph -of 35 USC 112, with respect to claims of the breadth sought here.
In recent cases we have recognized that the statutory requirement that the specification “describe the invention” might not be met even where the specification satisfies the related statutory requirement that it “enable any person skilled in the art * * * to make and use the same.” In In re Robins, 57 CCPA 1321, 429 F. 2d 452, 166 USPQ 552 (1970), in considering a possible rejection under the first paragraph of § 112, we stated that such a rejection
must be reversed inasmuch as the specification contains a statement of appellant’s invention which is as broad as appellant’s broadest claims, and inasmuch as the sufficiency of the specification to satisfy the “best mode” requirement of § 112 and to enable one shilled in the art to practice appellant’s process as broadly as it is claimed has not been questioned.
*927429 F. 2d at 456, 166 USPQ at 555 [emphasis added]. In In re Ahlbrecht, Patent Appeal 8411, decided January 7,1971, we held that the description requirement had not been satisfied as to a claimed class-of esters, even though the specification might have indirectly enabled one skilled in the art to make and use the entire class. It is clear from Robins and Ahlbreoht that it is possible for a specification to enable the practice of an invention as broadly as it is claimed, and. still not describe that invention.1 The first paragraph of § 112 requires-both description and enablement. What is needed to meet the description requirement will necessarily vary depending on the nature of the invention claimed. In Robins, as mentioned above, “a statement of appellant’s invention which is -as broad as appellant’s broadest claims”' was considered sufficient.
.It is the position of the Patent Office that the expression “a diamine” is too broad because the specification describes using only aliphatic and aromatic diamines and the expression would includeheterocyclic diamines. Appellants agree that -the expression includesheterocyclic diamines but contend that the description of diamines in the specification is as broad as the recitation in the claims. We agree. The specification states: “One of the objects of the present invention is to produce a polyimide reaction product of (1) a diamine, (2) * * * and (3) * * The specification later states: “The first reactant is a diamine which may be either an aliphatic diamine or an aromatic diamine” [Emphasis ours.] The solicitor would have us read “must”' for “may.” While we recognize that it is a common practice in drafting patent applications to use “may” in a mandatory sense, we note-that the originally filed claims, which are part of the disclosure, recited “a diamine” without further limitation as the first reactant. We therefore agree with ’appellant that “may” should be interpreted in this case as illustrative and not as limiting the description of diamines to aliphatic and aromatic diamines. The same "considerations apply to refute the solicitor’s contention that since the specific aliphatic diamines listed in the specification are saturated, the only aliphatic diamines described as reactants are saturated.
We turn now to the recitation of “a different dianhydride of an organic -tetracarboxylic acid.” The examiner held, and the board agreed, -that the specification described only tetracarboxylic acid anhydrides which were either saturated or -aromatic carbocyclics, and hence the description did not include 'heterocyclic di’anhydrides of *928tetracarboxylic acid. We find no basis for such, a conclusion. The specification states:
The third component used in the preparation of the polyimide reaction products of the -present invention is a different dianhydride of an organic tetracarboxylic acid. A comparatively limited number of such dianhydrides is available commercially and only a few -additional dianhydrides have been disclosed in the literature which are not available commercially insofar as it is known. Among the dianhydrides which * * * may be used * * * in the preparation of the polyimides of the -present invention are [seven listed earbocyclic dianhydrides] and the-like. [Emphasis ours.]
We find nothing in this passage which would limit the description of dianhydrides by excluding known heterocyclic-dianhydrides. The language used in listing the seven earbocyclic di’anhydrides is clearly illustrative and does not limit the broader description contained in the preceding sentences. Moreover, we note that the expression in •question appeared in the originally filed claims.
The decision of the board is reversed.