The aspect of a patent application that I most often need to explain to an inventor is the claim section. In an issued patent, the claims will appear at the end of the text and are usually preceded with a phrase, such as "I/we claim . . ." Most patents include a variety of claims.
Those claims that do not refer to another claim (such as claim 1, below) are "independent claims," while those that refer to another claim (reading, for example, "The method of claim 1, wherein . . . " or "The method of claim 1, further comprising . . .") and then specify something more are "dependent claims." The dependent claims accordingly incorporate the subject matter of the referenced claim and add something else to render the dependent claim at least somewhat narrower than the claim from which it depends.
Let's look at the following example set of claims directed to a brick-making process (please indulge me in accepting that the examiner finds them to novel and non-obvious) to illustrate these points:
1. A method for making a brick, comprising:
a) packing a composition including clay; and
b) heating the packed composition.
2. The method of claim 1, wherein the clay includes kaolin.
3. The method of claim 1, wherein the composition further includes lime.
4. The method of claim 1, wherein the packed composition is heated to a temperature of at least 1,000 deg. C.
5. The method of claim 5, further comprising:
c) holding the packed composition at 1,000 deg. C for at least an hour; and then
d) cooling the packed composition at a rate no greater than 50 deg. C per hour.
Assume we have 15 more claims in the form of additional method claims and product claims.
An inventor's first reaction upon reviewing the claims may be to object that he/she does not want to be limited to using kaolin and wants to cover processes in which the brick is fired at a temperature below 1,000 deg. C. If, for example another party (let's call them Pirate Brick) uses the inventor's process but substitutes another type of clay for kaolin, then Pirate will not literally infringe claim 2. That's a problem, right? Not necessarily. Assuming the patent issues, Pirate Brick need only infringe one of the claims in the patent to be found liable for patent infringement. Claim 1 does not specify any particular type of clay, so it may well cover Pirate Brick's process even if they use a different type of clay. If Pirate infringes claim 1 (or any of the other claims), they infringe the patent regardless of how many other claims Pirate may circumvent.
So why bother to include all of these narrower dependent claims if claim 1 is going to ensnare the most infringers? The answer is that a claim need not only be infringed by Pirate, the validity of the claim must also be upheld as valid. When the patent issues, the claims have a presumption of validity. Though, when you allege patent infringement against Pirate Brick, you can assume they will pay their lawyers a boatload of money to turn over every leaf to find additional prior art that was not considered by the examiner in an effort to invalidate your claims.
If Pirate Brick finds a good reference that covers a brick-making process closely on point to the inventor's process, Pirate may be able to invalidate claim 1 and some of the other claims. But if the brick was fired at a lower temperature or quenched at a faster rate in the earlier process, then claim 5 may still be upheld; and if Pirate Brick uses the temperature profile specified in claim 5, Pirate may still infringe the patent (via claim 5) even though they can invalidate claim 1.
Accordingly, each dependent claim can be viewed as a "fall-back" position in case our independent claim is too broad and accordingly held to be non-patentable or invalid. Pirate Brick may have an easier time invalidating claim 1 because it is so broad, though chances are that we can still distinguish the invention from whatever earlier processes Pirate may uncover based on at least one of the fall-back positions provided by the narrower dependent claims. If so, then the narrower dependent claims may survive; and hopefully Pirate will still infringe one of those surviving claims.
Consequently, I try to draft the claims to cover a range of broad and narrower embodiments, wherein different claims include different features that may help to differentiate the prior art, known or unknown (or satisfy other patentability requirements, such as enablement). Predicting which features will resonate with the examiner and help to establish patentability may also be difficult to forecast. If the examiner, for example, will only allow claims limited to the inclusion of kaolin, then we can evaluate whether to accept claims limited to kaolin or we can continue to argue or appeal in pursuit of broader claims. And that evaluation can be made at each stage of examination.
If the broadest claims are patentable and unassailable, then we may not need to worry about any of the narrower dependent claims (and whether they include very narrow limitations, such as requiring an imprint of Tickle-Me-Elmo riding a bicycle and drinking a bottle of Coca-Cola on a face of the brick), though in most cases, it is advantageous to keep narrower claims (assuming they are not ridiculous like the above Tickle-Me-Elmo example) to provide a second line of defense in case there is prior art (uncovered either during examination or in a post-grant challenge) that would force us to narrow our scope to remain novel and non-obvious over the prior art.
The ultimate compilation of claims will represent a balance of all of these considerations. And, of course, if you wish to discuss how your invention might be claimed, feel free to contact me to explore whether there may be a fit between your company/institution and Modern Times Legal. The above example, of course, is provided only for discussion and any actual legal advice regarding patent claims requires establishment of an attorney-client engagement and familiarity with the particulars of your invention.