From a lawyer's perspective, the "claims" are the most important component of a patent. A scientist or inventor will be more interested in the description that follows the claims, since it actually shows what the invention is and how it works. The claims, which more closely resemble gobbledygook to the average person, are what define the scope of the patent—which devices its monopoly will cover, and which devices will be unprotected. Infringement cases always revolve around the claims, not the description, although the description can help to clarify the meaning of the claims.
Here are the first seven claims in U.S. Patent No. 6,972,748, awarded to Microsoft a couple of days ago.
1. Method for inputting an information element from an information element set in an information processing device having a multiple axes input key movable in M multi-axial directions, said method comprising the acts of:
moving the key in one of the M multi-axial directions to generate a selection stroke;
repeating said act of moving the key N number of times to generate N selection strokes, a pattern of N selection strokes with each stroke being in one of M multiple-axial directions defining the information to be input to the information processing device; and
wherein the number of selection strokes N is given by a logarithmic value of a number of information elements in the information element set to a base M where M is the number of possible directions available from the multiple axes input key for each selection stroke.
2. The method of claim 1 wherein each act of moving comprises:
providing a selected subset of information elements from the information element set choices existing prior to the act of moving.
3. The method of claim 2 wherein the Nth stroke of the input key provides a final selected subset of information to be input to the information processing device.
4. The method of claim 3 wherein the information element set is a set of characters.
5. The method of claim 4 wherein the information processing device has a display screen to display the final selected subset of information as a character.
6. The method of claim 4 wherein the set of characters are alphabetic characters.
7. The method of claim 4 wherein the set of characters are numeric characters.
The first claim is an "independent claim," so called because it doesn't refer to any other claims. The next six claims are all "dependent claims." Claim 2 is dependent upon claim 1: if claim 1 is invalidated, claim 2 falls as well. Since 3 is dependent on 2, 3 would also be invalidated. And, by domino effect, the whole patent would be lost.
Note that all of the claims above are for methods. Microsoft couldn't patent the actual device in claim 1: it's a joystick, and they didn't invent the joystick. What they're patenting is a use for the joystick. A claim can also cover an actual device, like this claim from U.S. Patent No. 4,239,129 (1978):
1. A toy comprising an elongated housing having a chamber therein for a liquid, a pump including a piston having an exposed rod end extending rearwardly of said toy facilitating manual operation for building up an appreciable amount of pressure in said chamber for ejecting a stream of liquid therefrom an appreciable distance substantially forwardly of said toy, and means for controlling the ejection.
It's a water pistol!
The precise wording of the claim is very important. The holder of the water pistol patent, for instance, tried to sue Larami, claiming that their Super Soaker line was infringing the patent. The district court dismissed the suit because the Super Soakers had chambers outside the housing, thus making them fall outside the scope of the claim. See Larami v. Amron, 27 U.S.P.Q.2d 1280 (E.D. Pa. 1993).
Many other claims follow a "means plus function" structure, where they vaguely decribe a "means" for achieving some "function." For examples, see the means plus function node.