"At least", and support in the specification

Posted Wednesday, March 02, 2011.

Patent application drafters generally try to write applications that result in inventions being defined with a broad scope. A patent is essentially a property right, so wouldn’t an inventor would want the patent practitioner to try to acquire rights in the most property possible?

One way patent practitioners accomplish that is to sprinkle the term “at least” liberally through the application. For example, pretend that the bicycle had never been invented, and an inventor sought patent protection for the two-wheeled pedaled-vehicle. But it might be desirable to hold the property right for pedaled-vehicles with more wheels that might be invented in the future. Say, a tricycle for example.

To ensure the inventor receives protection for both the current bicycle, but also for future refinements in pedaled-vehicles that have additional wheels such as the tricycle, a patent practitioner might compose one of the patent claims like this:

A pedaled-vehicle, said pedaled-vehicle having at least two wheels.

I wouldn’t write a claim like that for various reasons, but it illustrates that the inventor’s bicycle having two wheels is encompassed by the claim, as is a tricycle invented by someone else in the future.

So is “at least” the best way to get an extremely broad patent? A recent U.S. District Court case shows what can happen if this is done carelessly. In MagSil v. Seagate, decided about two weeks ago in the District Court for Delaware, a claim using the term “at least” was invalidated because there was no support for the claim in the patent’s specification.

A patent specification must enable someone (not just any someone, but a PHOSITA, the meaning of which is a post for different day) to be able to make the patented invention. If the patent application contains “at least” in the claims, without there being a top end to the range, the specification must give some idea of how to construct the invention having virtually any number of whatever is being claimed. Otherwise, you haven’t properly told another how to make the device you are claiming.

In MagSil, the claim in question had a value for resistance, and the claim specified “at least” a certain resistance. At the time the claim was written, the inventor had no idea that technology would progress to the point that a version of the device with the high resistance used in the eventual device was even possible.

Years later, another company came up with a design for a high-resistance device that was technically within the range specified by the claim, and got sued for infringement. They successfully defended on the grounds that the inventor had not specifically detailed how to construct a device with that much resistance in the specification.

The moral of the story is that when using the term “at least,” it is important to reasonably bound the range with support in the specification for the range being claimed. Or, use claim language other than “at least” that still captures future variations.

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