The claims of a patent define the conceptual boundaries around an invention that the patent owner can claim as their own. The first claim defines the invention in the broadest possible terms so that no aspect of the invention is left out. However, patent applications are also drafted with a series of dependent claims that define selected aspects of the invention in more detail, saying in effect: “We now claim a more specific version of the invention.”

A detailed patent drawing rolled out on a desk

Why Use Dependent Claims?

Some clients, reviewing their patent application, will ask why dependent claims are needed at all. Generally, there are two important considerations that make dependent claims valuable:

  1. First, each dependent claim provides a more specific contingency position in case the broader claims are not allowed. This is somewhat intuitive once the client understands that the challenge is to draft a broad claim which protects all the minor variations of the invention to leave nothing ‘on the table,’ but also does not capture any prior art. This requires painstaking attention to how the claim is written. An “over broad” claim is one that inadvertently describes previously known technology, making the claim invalid because it covers prior art. A dependent claim, which narrows down an earlier claim, might define the invention without encompassing prior art, and so might be upheld even if the broader claim is invalidated.
  2. Second, a dependent claim can amplify the breadth of the broader claim. This is perhaps not as intuitive, but by providing a narrower focus from a preceding claim, the dependent claim may show what the preceding claim was not previously limited to.

Dependent Claim Example: Kids2 LLC v. Tomy International

A real-world example of the amplifying effect of a dependent claim can be found in the recent Federal Circuit decision Kids2 LLC v. Tomy International. Tomy had a patent on a bathtub for kids designed to work well for two stages of growth: infancy and toddlerhood. According to the patent, the tub had a separate seating area for each of those two stages, and the two seating surfaces had different inclined angles and were ‘joined’ at the bottom of the tub.

When Kids2 LLC sold a competing two-seater tub, Tomy sued them for patent infringement. However, Kids2 LLC won summary judgement of non-infringement before the U.S. District Court for Rhode Island, on two grounds, the court deciding that:

  1. The Tomy patent required the seating surfaces to be directly joined together (i.e., with no intervening structure), whereas the seating surfaces in the Kids2 tub were not directly connected.
  2. One of the seating surfaces in the Kids2 tub had a horizontal seating surface, but the Tomy patent did not say that either seating surface could be horizontal.

On appeal by Tomy, the Federal Circuit reversed the lower court’s ruling. On the question of whether the seating surfaces had to be directly connected to each other, the appeals court noted that dependent claim 18 defined an embodiment in which seating surfaces were joined by an intervening structure. The court noted that “Independent claim 1 must be broad enough to contain the full scope of its dependent claims, including claim 18.” 

In this way, claim 18 amplified the understanding of claim 1 as allowing either direct or indirect connection between the seating surfaces. Accordingly, even though the Kids2 tub did not have the specific indirect joining structure of claim 18, that claim showed that claim 1 could cover that tub, regardless of the type of specific intervening structure joining the seating surfaces.

Regarding the horizontal seating surface that Kids2LLC asserted took their tub outside the Tomy patent claims, the court noted that claim 17 said that one of the surfaces could be ‘generally horizontal, and in addition, various dependent claims mentioned specific angles at which seating surfaces might be disposed.  The language in these dependent claims was taken by the court as indicating that claim 1, which did not specify angles of inclination, also did not exclude any particular angle, including a zero angle.

Thus, the Federal Circuit Court of Appeals has shown that dependent claims in a patent can be strategically drafted to not only provide fallback positions in case the broader claims are too broad, but also that dependent claims can amplify the breadth of the broader claims.

For Tomy, dependent claims may have saved the bathtub as well as the baby.

Final Thoughts

The Tomy case illustrates how dependent claims play a valuable role in interpreting a broader independent claim in a patent, in addition to providing a fallback position of more narrow scope. 

They help ensure that key aspects of an idea are protected even if the broadest claims face challenges.

Frederick Spaeth

Any examples are solely for educational and illustrative purposes. They do not constitute legal advice and should not be construed as recommendations for specific actions. For personalized legal guidance, please consult a qualified attorney.

This article is for informational purposes, is not intended to constitute legal advice, and may be considered advertising under applicable state laws. The opinions expressed in this article are those of the author only and are not necessarily shared by Dilworth IP, its other attorneys, agents, or staff, or its clients.