The Role of Dependent Claims

Patent claims define the scope of rights for an invention.

A claim that defines the invention by itself is called an independent claim.
It describes the main idea of the invention — the “core” claim.

A claim that depends on an independent claim is called a dependent claim.
Dependent claims limit or narrow the scope of the independent claim.

Most patents include several claims arranged in multiple levels.

 
Compared with independent claims, dependent claims cover a smaller range of protection.
But in return, they are more likely to be approved by the Patent Office because they can avoid rejection more easily.

When filing a patent application, the basic strategy is:
1. Write independent claims as broadly as possible, and
2. Add several dependent claims with different levels of limits — such as “this might pass,” “this should pass,” or “this will definitely pass.”

There are two main types of dependent claims:
External addition and Internal addition.

External Addition: Adding New Elements

A dependent claim of the “external addition” type is a claim that adds a new element to the independent (higher-level) claim.

・Claim 1 (independent): A + B
・Claim 2 (dependent claim): A + B + C
In this structure, Claim 2 adds the component (C) to the combination of A and B in Claim 1.

If the independent claim for a smartphone describes “a device including a touch panel (A) and a display (B),” then the dependent claim with external addition might further include components such as an accelerometer (C) or a fingerprint recognition unit (D).

If prior art (a cited reference) already shows A and B, Claim 1 cannot be patented.

However, for Claim 2 (the dependent claim with external addition), it can be argued that “the cited reference does not disclose element (C)” and that “adding (C) to (A + B) produces a unique effect.” Therefore, Claim 2 has a greater possibility of being granted a patent.

In short, external addition builds the invention by stacking new parts on top of the minimal structure described in the independent claim.

Internal Addition: Making Elements More Specific

A dependent claim of the “internal addition” type is a claim that expresses the elements of the independent (higher-level) claim in more specific terms.

・Claim 1 (independent claim): A + B
・Claim 2 (dependent claim): aX + B (where aX is a more specific form of A)
In this structure, Claim 2 narrows element (A) in Claim 1 by defining it more specifically as (aX).
 
For instance, if the independent claim lists “a sensor (A)” as a component of a smartphone, the dependent claim may limit this to “an accelerometer (aX).”
The accelerometer (aX) is a more specific version, or a sub-concept, of the general sensor (A).

If the cited reference discloses (aY) and (B) — where (aY) is a specific example of (A) — then Claim 1 (the independent claim) cannot be patented.
For instance, if (aY) in the cited reference is a “temperature sensor,” that temperature sensor (aY) is one type of sensor (A). Therefore, the cited reference is considered to describe the sensor (A) in Claim 1.

However, for Claim 2 (the dependent claim with internal addition), the applicant can argue that “the cited reference does not disclose (aX)” and that “using (aX) instead of (aY) produces a distinctive effect.” Therefore, Claim 2 has a higher chance of being granted a patent.

In addition:
– Claim 2 (dependent claim with internal addition): A + B, where A includes a1 and a2.
– Claim 2 (dependent claim with internal addition): A + B, where A is attached to the side of B.
These kinds of claims, which describe the structure or condition of an element in the independent claim in more concrete terms, can also be regarded as a form of internal addition.

In short, internal addition expresses the same invention in more detail, step by step.

Balance Between External and Internal Additions

Which type is used more often in real patent applications?

As one case study, we randomly selected several recent patents filed by Mazda and examined the ratio of dependent claims using external and internal additions.

External additions: 18 claims (14.9%)
Internal additions: 100 claims (82.6%)
Difficult to categorize: 3 claims

Across 22 patent applications containing a total of 121 dependent claims, about 80% were classified as internal additions.

The data for Nippon Steel were as follows:

External additions: 11 claims (9.6%)
Internal additions: 104 claims (90.4%)

Among 19 applications with a total of 115 dependent claims, roughly 90% were internal additions.

For reference, we also conducted the same review for our own organization (INTERBRAIN IP Attorneys):

・External additions: 40 claims (28.4%)
・Internal additions: 101 claims (71.6%)

Across 30 patent applications including 141 dependent claims, about 70% were internal additions.

Overall, internal additions tend to be used more frequently than external additions.
 

Making a “Useful” Patent

Both external and internal additions are techniques used to increase the likelihood of a patent being granted.

That said, even if a patent application includes many dependent claims and one of them leads to allowance, the patent will have little value if that dependent claim cannot put any pressure on competitors.

If a competitor tries to avoid your patent, allowed dependent claims can still have power when:
– It’s almost impossible to avoid;
– It can be avoided, but that would hurt the product’s quality or appeal;
– It can be avoided, but that would raise production costs a lot.

On the other hand, if your dependent claims are easy to avoid, they don’t add real value — even if they were granted.

While aiming for the broadest possible scope in the independent claim, multiple dependent claims should be prepared with varying numbers of components and levels of abstraction.
By fine-tuning the claim scope through amendments, one can seek the optimal balance between “obtaining a patent” and “making the patent effective in practice.”