What Are Independent And Dependent Claims?

All patent claims are either independent or dependent. Independent claims stand alone, and do not reference any other claim. Thus, in the following claim set, claim 1 is independent because it does not reference any other claim.

1. A chair having only two legs.

2. The chair of claim 1, further comprising at least one leg made of wood.

3. The chair of claim 2, wherein at least a portion of the chair is covered with a fabric.

When filing a new patent application, claim 1 should always be independent. During prosecution, of course, claim 1 might be canceled or withdrawn, or it might be amended to recite dependency on a higher numbered claim. No matter. The examiner would renumber the claims prior to issuance so that the first independent claim is once again numbered claim 1.

Dependent claims reference another claim and are proper subsets of their parents, i.e. the claim(s) upon which they depend. Continuing with the example above, claim 2 is dependent because it references claim 1. Dependent claims include all the limitations of the referenced claim. To infringe claim 2, a competitor's chair would not only have to have at least one leg made of wood (the limitation stated in claim 2), but it would also need to have only two legs (the limitation imported by reference to claim 1). Dependent claims can be dependent on either an independent claim, or on another dependent claim. In the example above, claim 3 might is dependent on claim 2, and includes all of the limitations of claim 3, plus the limitations of claim 2, plus the limitations of claim 1.

Dependent claims can depend on any other claim, even if that parent claim has a higher number. Thus, claim 2 could be dependent on claim 5 or 7, even though those claims appear later in the listing. Having a claim dependent on a higher number claim often occurs during patent prosecution as a result of cancellation of claims. For example, claim 2-10 could be dependent on claim 1, and then claim 1 is canceled or withdrawn. The applicant may then add a new claim 18, and amend claims 2-10 to be dependent on claim 18. Even claim 1, which is traditionally an independent claim, could be made dependent on another claim (say claim 15). When the patent is issued the patent office will renumber the claims to put them in a logical order.

Since dependent claims are proper subsets of the claim(s) upon which they depend, people often ask why they are useful. After all, in the example above, a competitor would escape infringement by producing a chair with four legs, i.e. circumventing a limitation from claim 1, regardless of whether the competitor's chair has wood legs or has a fabric covering. The answer is twofold.

First, dependent claims provide fallback positions during prosecution and enforcement actions. If claim 1 were filed today, for example, it would be anticipated because two-legged chairs have been around for decades. Even if claim 1 somehow made it past the patent office, and issued in a patent, the claim would be invalidated over the prior art during litigation. If claim 1 were the only claim in the patent, the case would be over and the patentee would lose. Claim 2, however, recited the additional limitation that the two-legged chair must have a wooden leg. That claim might well be patentable because the prior art always used metal legs. Thus, inclusion of claim 2 in the patent application would have provided valuable fallback positions in case claim 1 were invalidated. The same is true for claim 3. Even if claims 1 and 2 are invalid over the prior art, it may be that the only two legged chairs with wooden legs were made entirely of wood, and had no fabric covering. In that case claims 1 and 2 would be invalid, but claim 3 would still be valid. In short, inclusion of dependent claims in a patent application can provide useful fallback positions during patent prosecution, and then later on during litigation.

The second major benefit of dependent claims is that they help ensure broad interpretation of the claims upon which they are dependent. Consider the following claim:

1. A method of making money for an author, comprising:

writing a book on patenting that includes at least 90 indexed figures;

publishing the book through a publisher, and receiving a royalty that provides sufficient income to meet the author's reasonable household expenses without incurring debt.

In interpreting this claim one might wonder how much royalty is sufficient to meet the author's reasonable household expenses. Presumably that would be an issue of fact at trial, but it could be argued that "reasonable expenses" are no more than say $5,000 - $10,000 a month. If, however, the applicant filed additional dependent claims, the fact that the dependent claims are proper subset of independent claim 1 necessarily means that claim 1 is broader in scope than any of the dependent claims. That wouldn't change the scope of claim 1, but it may well help the court to properly interpret claim 1.

2. The method of claim 1, further comprising the author having a house that is at least 1500 sq. ft.

3. The method of claim 1, further comprising the author purchasing a house with three acres of land, a 7500 sq. ft. house, a pool, a stable, and a guest house for live-in maintenance help.

4. The method of claim 1, further comprising the author having a spouse and three children in the household.

5. The method of claim 3, further comprising each of the three children attending college at private universities.

This can be shown graphically. The Venn diagram below depicts claims 1 and 2. Since claim 2 is a proper subset of claim 1, the oval for claim 2 is depicted as smaller than, and positioned completely within the circle of claim 2.

Figure 32 — Dependent Claims Are Proper Subsets Of Their Patents

The inclusion of claim 3, however, requires the term "reasonable household expenses" must be interpreted broadly enough to support a 7500 sq. foot house, not merely a 1500 sq. foot house. Similarly, the inclusion of claims 4 and 5 requires the term "reasonable household expenses" to be interpreted broadly enough to include having a spouse, and sending three children to college at the same time. So to reiterate, adding dependent claims doesn't change the scope of the claims upon which they are dependent. But their inclusion in applications and patents helps the court properly interpret the parent claims in a broad fashion.

Figure 33 — Dependent Claims Help In Interpreting The Independent Claims