Claim Interpretation in Patent Application Drafts

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Reading and understanding the claims in a patent application is important as the claims define the limits of what the patent covers, and what it does not cover.  Not only do the claims determine if another product or process infringes the patent, they are also used to differentiate over prior art in order to obtain the patent in the first place.

Interpreting claims is not an easy task due to the legalistic manner in which they are written.  To reduce costs of obtaining patent protection, while ensuring the resulting patent provides desirable coverage, it can be beneficial for inventors to be armed with an understanding of the basic structure of claims, as well as what to look for when reviewing claims. Likewise, assisting inventors in understanding the meaning of claims during prosecution can help ensure that issued claims cover commercial embodiments or, potentially, accused products or methods.  The following provides a basic overview of claim interpretation intended for use by inventors when reviewing a patent application draft.

Basic Structure of Claims

A claim is a sentence, often written in paragraph form as illustrated below, that starts with the type of claim, called the preamble, followed by a transitional phrase and elements of the claims.  Most patents include several claims, numbered sequentially, including one or more independent claims and a series of dependent claims.  An independent claim stands alone, whereas a dependent claim further narrows an independent claim.  The following is an example of independent claim for an adhesive bandage, which stands on its own:

  1. A compressive dressing which may be used to treat a finger, hand, toe, foot, limb, torso or head wound or a surgical site comprising:

a conformable, porous, self-adhering elastomeric substrate wherein the substrate does not adhere to clothing, hair or skin and which has a compressive force when extended that is sufficient to hold the dressing in place for a period of time to provide a therapeutic effect to the wound; and

an absorbent layer flexibly bonded to the self-adhering substrate using a thin strip of adhesive positioned between the absorbent layer and the substrate allowing the elastic substrate to expand and contract by sliding past the pad.

The preamble is “A compressive dressing which may be used to treat a finger, hand, toe, foot, limb, torso or head wound or a surgical site”, the transitional phrase is “comprising:” and the elements are “a conformable, porous, self-adhering elastomeric substrate…”, and “an absorbent layer flexibly bonded to the self-adhering substrate…” The preamble usually sets out the type of claim, which is generally categorized as a product (e.g., apparatus, as in the above example, device, or system), or a process (e.g., method or use).  The preamble may also list elements which are not part of the claimed invention, but are needed to define or supply support for the elements of the claim (for example, the language “to treat a finger, hand, toe, foot, limb, torso or head wound or a surgical site” is included in the preamble so that the claim can later recite how the dressing may be applied to these parts of the body). Normally, the preamble does not limit the claim, but in some instances it can when necessary to make sense of the claim.

The connecting or transitional phrase (i.e., comprising) links the preamble to the elements of the claim.  While it may seem that transitional phrases are not important, they can impact the claim’s meaning as they specify whether the claim is limited to only the elements that are listed or anything that includes at least the elements but may include other things as well.  “Comprising” or “which comprises” is an open-ended term which means that the claim encompasses all elements listed but can include additional unnamed elements.  “Consisting of” is closed ended, meaning the product or method must have all the elements and no more.

Understanding Claims When Reviewing a Patent Draft

When reviewing a patent application, inventors should review the claims to ensure the claims capture what the invention is, or in other words, what the inventors consider to be new.  It is important for inventors to understand the following:

Claim Scope

Inventors should be aware that claims are often drafted to be open-ended (i.e., include all elements but can include additional things). Keeping this in mind, review should concentrate on verifying that the elements of the claims include at least one element that is believed to be new.  The first independent claim is often the broadest claim in the patent, with subsequent independent claims adding additional or different features.  Inventors should focus on verifying that the first listed independent claim does not include elements that are not needed to distinguish over what has already been done, or elements that are not used in each implementation of the invention.  However, caution should be exercised.  A well drafted patent claim should only list those aspects that are considered new for the industry, as opposed to every aspect of the product/process being patented.

Meaning of Terms

Terms in the claims should normally be given their ordinary meaning. However, the patentee is also “his own lexicographer”, meaning that the patentee can include definitions of terms in the specification of the application that can be more restrictive or have different meaning other than their ordinary meaning.  When looking at the meaning of elements or terms in the claims, the inventors should first consider what the term would ordinarily mean and then look to the specification for any definitions that may further limit or define the term.  While the patentee can be his own lexicographer, the definition must be clear and may not contradict the ordinary meaning or broaden the definition to the point of meaninglessness.  For example, one could not state that “the term ‘liquid water’ includes states of water that are not liquid”.

BRI Test

When prosecuting the patent with the United States Patent and Trademark Office, examiners use a “broadest reasonable interpretation” (BRI) test for interpreting claims.  Under the BRI test, the claims are interpreted “in light of the specification” as would be understood by one of ordinary skill in the art.  In practice, examiners often give little weight to the “in light of the specification” portion of the BRI test, which can result in broad interpretations of claim terms.  Even so, an inventor’s careful attention to definitions provided in the specification is vital as the specification provides support for potential claim amendments, arguments that the claims don not need to be amended, and may be used against or in support of the patent owner when trying to enforce the patent.

Claim Differentiation

Dependent claims, as well as other types of independent claims in a patent application, are used to provide claim differentiation and to potentially capture different types of infringers.  Consider that one type of infringer may be a manufacturer of a widget and the other is the user of the widget.   Using the above example, a first independent claim may be drafted to capture the manufacturer of the widget and the second independent claim is drafted to capture the user of the widget.  Independent and dependent claims are drafted to capture each type of activity.  Dependent claims depend from independent claims and only have meaning when combined with the elements of the independent claim.

Dependent claims, and sometimes later independent claims, can provide further limitations of elements in the independent claims or preceding independent claim under the principle of claim differentiation.  The principle of claim differentiation provides that there should some difference between claims.  For example, if a dependent claim further refines that a “biological sample” in the independent claim includes “saliva”, under the principle of claim differentiation the “biological sample” in the independent claim must include more than saliva.  If not, there would be no difference between the independent and dependent claims.  For this reason, and as the independent claims are not limited by the dependent claims, often times dependent claims are drafted to capture specific implementations of the invention.  Such drafting tactic, of drafting dependent claims that do not cover all implementations of the invention, is legally beneficial and supports a position that the independent claims cover additional implementations.  As an example, consider an invention of a microfluidic chip used to process biological samples containing nucleic acids.  Some designs of the microfluidic chip include one continuous channel and others include branching channels.  The independent claim may state that the microfluidic chip includes at least one channel and dependent claims may clarify that the at least one channel includes a continuous channel or a plurality of channels.


Patent claims must particularly point out and distinctly claim that which the inventor regards as the invention.  To that end, claims must be drafted as clearly as possible, and using language from the patent application itself.  For instance, in the example above, if the independent claim recites a “biological sample”, additional language in the claim such as “biological sample (e.g., saliva)” would make it unclear whether the claim was directed to just saliva or additional types of biological samples, and therefore should be avoided.

Arming inventors with the requisite tools to properly review claims in a patent application draft is an effective way to reduce costs of filing and obtaining the patent.  Such knowledge can reduce the writing efforts between the drafting patent attorney and the inventors while ensuring that the resulting patent provides desirable coverage for the patent owner.  Additionally, the inventors can assist in drafting claims that capture subject matter which differentiates over known prior art, which can reduce the number of communications with the United State Patent and Trademark Office prior to receiving an allowance.

We invite you to contact us for more information and other assistance in addressing issues relating to patent applications, patent infringement and patents in general.


© Crawford Maunu PLLC.  All rights reserved. This material is for informational purposes only and should not be construed as legal advice. Communication of this material is not intended to establish an attorney-client relationship. Legal advice should be sought from legal counsel.