2.4 Alternative Elements and Markush Claims
In many jurisdictions, a single patent claim can contain alternative elements. In everyday language, the term “or” is typically used to indicate alternatives. However, in patent drafting especially within claims phrases such as “metal or plastic” are generally considered unclear or ambiguous. Where permitted by national practice, expressions such as “metal and/or plastic” or “at least one composition selected from metal and plastic” may be employed to express an inclusive “or.” By contrast, when an exclusive “or” is intended, the wording “either metal or plastic” should be used.
To incorporate multiple exclusive alternatives within a single claim, a specific claim structure commonly known as a Markush claim (named after the inventor associated with the case in which this drafting style first appeared) is recognized in many jurisdictions. The Markush format can significantly simplify the work of a patent drafter when preparing a comprehensive set of claims (see Section 3 on claim sets and dependent claims). Both independent and dependent claims may contain alternatives, provided that the quantity and manner of presenting these alternatives do not make the claim unclear or difficult to understand.
The typical wording used in a Markush claim is:
“… wherein element A is selected from the group consisting of X, Y, and Z.”
Example
A chemical process can be performed with either “copper,” “lead” or “gold.” The patent drafter might consider using a broader, more abstract term that encompasses these three options, such as “metal,” but neither the patent drafter nor the inventor may be certain that the process would function with any metal. Indeed, the inventor may know with certainty that the process would not operate with mercury. Consequently, the patent drafter cannot simply use the broader term “metal” without additional qualification.
The patent drafter and the inventor may not identify a more suitable general term that accurately covers only the three metals that are compatible with the invention. One option would be to draft three independent claims one directed to “copper,” one directed to “lead,” and one directed to “gold.” However, by using the Markush format, the patent drafter can instead prepare a single independent claim stating “a metal selected from the group consisting of copper, lead and gold.”
The use of Markush groups is not confined to chemical inventions; they may also be applied in other technical areas, for example “a fastener selected from the group consisting of a nail, a screw and a rivet.” In practice, however, Markush groups are often neither preferable nor necessary in such fields, since generic terminology describing the alternative elements (e.g., “a fastener”) or functional language (e.g., “a fastening means”) typically provides a broader definition of alternatives.
By contrast, Markush groups are frequently used in chemical claims to define, for instance, alternative chemical ingredients that may be included in a composition, alternative steps within a chemical process, or alternative values for radicals within a formula. In product claims that structurally define a group of chemical products through a general formula, the use of a Markush formula is very common.
Example
Claim 1. A compound of the formula:
Figure 1
wherein
- R1 is selected from the group consisting of H, C1-C3 alkyl, C3-C5 cycloalkyl and C1-C3 perfluoroalkyl;
- R2 is … ; R4 is … ; R5 is … ; R6 is … ; and
- R7 and R8 are each independently H, C1-C4 alkyl, (C1-C3 alkoxy)C2-C4 alkyl or hydroxy C2-C4 alkyl;
- and pharmaceutically acceptable salts thereof.
This claim encompasses the structurally defined compounds obtained from all possible combinations of radicals R1–R8 (as defined by the eight corresponding Markush subgroups), together with the salts of these compounds formed with any acids that are non-toxic to animals or humans (as defined by the functional expression “pharmaceutically acceptable salts thereof”).
As with any other claim, a Markush claim must comply with the requirement of unity of invention.
Multiple Selections within a Markush Group
If the patent drafter intends to allow the simultaneous selection of more than one member from a Markush group (rather than limiting the selection to a single member), this must be expressly stated in the claim. Otherwise, the claim will generally be interpreted as permitting only one selection at a time.
For example, the phrase:
“wherein the solvent is selected from the group consisting of A, B, and C”
is understood to mean that only one of A, B, or C can be used as the solvent. It does not permit the use of a combination of two or more of them.
If the invention allows or requires the simultaneous use of multiple members, the claim must clearly indicate this possibility, for instance:
“wherein the solvent is selected from the group consisting of A, B, C, and combinations thereof.”
or through an equivalent formulation accepted in the relevant jurisdiction.
A Markush group must be clear and unambiguous, and the drafter should verify that its use represents the most suitable method for defining the claimed invention. In the previous example, if iron were also suitable for use in the invention, the claim as drafted would not cover embodiments that employ iron. The drafter must therefore exercise care to ensure that all patentable embodiments of the invention are properly encompassed.
Markush groups should be used with particular caution. If any of the listed alternatives are disclosed in the prior art, the entire claim may be considered to lack novelty. Although a Markush claim can provide an efficient approach for drafting an independent claim that fulfills the unity of invention requirement, in practice it may sometimes be preferable to claim each member of the group separately through a set of dependent claims (see Section 3 of this module).
2.5 Functional Elements and Means Plus Function Claims
As illustrated earlier, functional language can be used to define a claim element based on what it does that is, by the function it performs rather than strictly by its structural characteristics. In general, a functional element may be included in a claim provided that a person skilled in the art would be able to carry out the specified function without the need for inventive activity.
Functional definition can be expressed in several ways:
-
The element may be defined directly by its function, for example:
-
“a computer-readable storage medium,”
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“an oxidizing agent,” or
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“a pharmaceutically acceptable excipient.”
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The element may be identified using a generic structural term that inherently conveys its function, such as:
-
“a heater,”
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“a fastener,” or
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“a solvent.”
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Functional language may also be introduced immediately after the relevant element through a descriptive phrase, such as:
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“providing [some operation]”;
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“creating [some physical or chemical property]”;
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“such that [something is achieved]”;
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“whereby [some effect happens]”;
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“so that [some end is achieved]”; or
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“configured to [achieve some result].”
Among the different approaches to functional claiming, means plus function claims define elements not by their precise structure but rather by the means for performing the function disclosed in the specification. In this claim format, structural detail is replaced with a functional description, while the specification provides the supporting disclosure that defines what the “means” actually includes.
The interpretation of means plus function claims varies among jurisdictions, and even within a single jurisdiction the prevailing interpretation may evolve over time. For instance, some patent offices and courts construe such claims as covering only the specific means disclosed in the patent specification for carrying out the stated function, along with their reasonable equivalents. Accordingly, the scope of protection does not necessarily extend to every possible mechanism capable of performing the function; instead, it is limited to what is sufficiently supported by the description.
Because the claimed element is defined functionally rather than structurally, means plus function claims can be interpreted either broadly or narrowly, depending on how courts assess the relationship between the claim language and the specification. In infringement litigation, considerable attention is often devoted to determining whether a disputed claim should be classified as a means plus function claim in the first place, since that determination can significantly influence both the scope and enforceability of the claim.
The conventional form of a means plus function claim uses the word “means” followed by a description of the function it performs. For example, in the case of a rice cooker invention, a claim drafted using means plus function language might read:
- An apparatus for cooking rice, comprising:
- a means for holding rice; and
- a heater configured to heat the rice-holding means.
In this rice cooker example, rather than explicitly identifying a particular structural component (for instance, “a bowl”), the claim refers to a device that performs the function of holding rice. This formulation avoids restricting the claim to a specific structure and thereby reduces the possibility that competitors could circumvent infringement by adopting a different rice-holding device that performs the same function.
Not every element within a means plus function claim must itself be drafted as a “means.” Each element of the claim can be treated independently. Suppose a claim contains three elements two written in means plus function language and one expressed as a specific structural element such as a “heater.” The structural element will normally be interpreted according to its ordinary meaning as understood by those skilled in the art, whereas each means plus function element will be analyzed through two steps:
1 - First, determine the function explicitly recited in the claim, and
2 - Then, identify the corresponding structure disclosed in the specification that performs that function.
Means plus function claims can be particularly advantageous in jurisdictions where courts interpret them more broadly than claims defined purely by structure. Even in legal systems that do not adopt such a broad interpretation, these claims still provide benefits because they are construed differently; this distinction, regardless of its precise scope, expands the overall protection when a patent application contains both structural claims and means plus function variants directed to the same invention.
It is also important to bear in mind that judicial interpretations evolve over time. Given the typical patent term of 20 years, a claim that is interpreted narrowly during the early years of a patent may later be construed more broadly. Including a well-balanced combination of claim formats at the time of filing can therefore provide valuable long-term flexibility.
Irrespective of the claim format used, the specification must contain a sufficiently detailed written description that clearly identifies the structure or structures capable of performing each recited function. Failure to provide such support may result in invalidity or an unduly narrow interpretation. The drafter must ensure that adequate structural support is disclosed for every functional element; this principle applies to all types of claims, not only means plus function claims.
Another important drafting consideration is avoiding two opposing pitfalls:
1 - Excessive structural disclosure, in which numerous or irrelevant structures are listed, may introduce ambiguity and lead to restrictive interpretation; and
2 - Insufficient identification, where the specification fails to clearly define which structures perform the claimed function, may allow an alleged infringer to argue that only a very limited subset of structures is covered.
For example, if a claim recites “means for fastening,” the specification should clearly identify such means, for instance “tapes, adhesives, rivets, or any combination thereof.” Without such clarification, courts may construe the phrase “means for fastening” far more narrowly than the inventor intended.
If a claim defines all of its elements solely in functional terms whether through means plus function wording or other forms of functional language it risks rejection as an attempt to claim a mere desideratum, meaning a desired outcome without specifying the mechanism by which it is achieved. The claimed subject matter must always be defined with as much precision as the invention reasonably permits.
Finally, it is entirely acceptable and often strategically beneficial to include within a single patent both means plus function claims and claims that do not rely on such functional language. This approach provides complementary and layered protection, accommodating different interpretative approaches across jurisdictions and over time.
3. Claim sets
A patent specification generally contains more than one claim. Consider the following example:
- A device, comprising:
- a pencil; and
- a light attached to the pencil.
- The device recited in claim 1 wherein the light is detachably attached to the pencil.
- The device recited in claim 2 wherein the pencil is red in color.
A typical patent specification contains independent claims (also known as main claims) together with one or more dependent claims (or subsidiary claims). Dependent claims, which refer to preceding claims, further define and refine the scope of the invention.
3.1 Independent Claims:
Every patent application must contain at least one independent claim that defines the essential features of the invention. These elements represent the core aspects necessary to satisfy the legal requirements for patentability, such as novelty and inventive step.
3.2 Dependent Claims:
An independent claim may be followed by one or more dependent claims. These dependent claims provide additional detail regarding specific embodiments of the invention described in the independent claim. A dependent claim incorporates all the features of the claim or claims to which it refers, even if those features are not explicitly repeated. In some cases, a dependent claim may specify a feature that applies to several preceding claims (whether independent or dependent). Accordingly, a dependent claim may refer back to:
- One or more independent claims.
- One or more dependent claims.
- A combination of both independent and dependent claims.
Claim Quantity and Strategic Drafting
Patent applications containing only a single claim are relatively rare. This is largely because patent drafters typically seek to obtain broad and flexible protection by including claims with different scopes that address various aspects of the invention. Although most patent laws do not prescribe a strict upper limit on the number of claims, drafting an excessively large number of claims is generally discouraged, primarily because of the additional costs incurred by the client.
When preparing a claim set, patent drafters must take several factors into account:
1- Official Fees: Many patent offices charge additional filing fees when the number of claims exceeds a specified threshold. These claim fees are frequently non-refundable, even if the number of claims is later reduced through amendments. In addition, other official fees, such as examination and grant fees, may also depend on the number of claims included in the application. The method used to calculate these fees varies among offices: some count only the numbered claims, whereas others such as the United States Patent and Trademark Office (USPTO) impose additional fees for each claim drafted in multiple dependent form, regardless of whether that claim is separately numbered.
2- Scope and Utility: Drafting claims that are either excessively broad or unduly narrow can undermine the effectiveness of patent protection.
- Overly Broad Claims: Such claims are more likely to be rejected for failing to satisfy the requirements of novelty or inventive step, because their scope encompasses prior art.
- Overly Narrow Claims: Even if granted, these claims may provide limited practical benefit, since competitors can easily design around the restricted scope and thereby avoid infringement.
3- Clarity and Complexity: Patent laws generally require claims to be clear and concise. An excessive number of dependent claims can introduce unnecessary complexity. Accordingly, the overall number of claims should remain proportionate to the character and complexity of the invention being claimed.
The Secretariat of WIPO assumes no liability or responsibility with regard to the transformation or translation of the original content. World Intellectual Property Organization (WIPO) (2023). WIPO Patent Drafting Manual, Second edition. Geneva: WIPO. DOI: 10.34667/tind.44657