Ask twenty people to write a program and give them the same specifications, and you'll get 20 very different programs. Much like English, there are often many ways to say something. "The cat chased the dog." "The dog was chased by the cat." "The domesticated canine was pursued by the domesticated feline." Software is similar; the same basic concept may be expressed in many, many different ways.
If a patent was granted only on the specific code written by the patent applicant, then software patents would not pose a threat of any kind to anybody; the odds of exactly replicating somebody else's code are astronomical. Unfortunately, software patents are being granted on effects of code, and not the code itself! Consider Amazon.com's famous "One-Click Shopping" patent. When Amazon.com successfully sued Barnes & Noble for having a similar feature and thus violating their patent, exactly how did Barnes & Noble violate Amazon.com's patent? Well, they certainly didn't sneak over during the night and steal the code from Amazon.com's servers. Odds are, given the different setups of Amazon.com and Barnes & Noble, the One Click Shopping system was implemented almost completely differently, quite probably in different languages on different hardware platforms and different integrations with different databases. It is possible that no two lines of code written by the companies is the same. It obviously has nothing to do with the code.
If it was not the code... then what else is there that Barnes and Noble could have violated? The only conclusion one can come to is that Amazon has successfully patented the entire concept of one-click shopping. If this seems surprising, or an unlikely conclusion, it's not. Richard Stallman, the founder of the Free Software movement and a man who has been programming for decades, wrote an essay called The Anatomy of a Trivial Patent, in which he dissects a very normal software patent. Where physical patents include precise descriptions of components, their shapes and relationships, software patents are written so broadly that they essentially lay claim to entire concepts. A sample from the essay:
Patent excerpt: "using a computer, a computer display, and a telecommunications link between the remote user's computer and the network web site,"
Stallman: "This says they are using a server on a network."
Because computer programs are interconnected with so many other computer programs and hardware devices, it does not take much work at all to expand a trivial idea like One-Click Shopping into an impressive looking patent application that no patent officer is trained to handle. If you read Stallman's essay, you'll find that the actual subject of the patent application takes up very little space; it has to be fluffed up with other irrelevant tripe to take up more then two sentences (and it's hard to make two sentences look like a non-obvious invention).
I challenge anybody who thinks this is incorrect to come up with a rigorous and useful metric for determining whether a given piece of software is covered by a given patent without making any reference to the final functionality of the piece of software. Remember that determining if a given machine violates a patent explicitly does not reference the functionality of the machine, only the design itself.
In fact, patent law is supposed to encourage multiple implementations of the same process! Take a simple example: The turn signals in a car. There are quite a few designs for the turn signal controls, some just working the turn signal, others integrating cruise control or windshield wiper controls. Designing a good turn signal control is non-trivial; while the basic requirement of moving a stick to activate an action is simple in concept, designing a cost-effective switch that will last the lifetime of the car, during which the switch will be used thousands upon thousands of times, in all manner of environmental conditions, and with death or serious injury potentially on the line if the switch malfunctions, is not trivial. Thus, when solutions are found, they are patented. However, there are several variations on the theme that have been developed. Sometimes the auto manufacturer wants a new one to fit in better with the theme of the car, sometimes the car company thinks it will be cheaper to make their own then license one from a competing car company. Thus, there is a reward for creating a new device, both because you can use it and you might get licensing revenues, and incentive for the competition to come up with new designs that will benefit them if they believe the licensing is too expensive. That's capitalism.
But suppose you could apply for, and receive, a patent for "The use of a stick-like object to activate multiple actions, depending upon the direction in which it is moved"? And get the patents for the two basic behaviors, which are "stick", which is when you turn on a turn signal and the stick stays in that position until the signal comes off, and "toggle", which is when you pull back on the stick to toggle the brights on or off. This is what is occurring in the software patent arena. Now, whoever owns that patent completely owns the idea of "turn signal sticks" (along with a wide variety of other things, such as some gaming joysticks). There is no incentive for the competition to try to build their own, because there is no way to build a turn signal stick that won't be a turn signal stick.
Going back to my sentence example, try communicating the concept of "chase" without communicating the concept of "chase". "Pursued with the intent of catching?" "Following more and more closely, in the attempt to occupy the same space?" You can't. If you want to create a One Click shopping competitor, you can't, because no matter how different it is from Amazon.com's system, it will always still be a One Click Shopping system. This is more evidence that Software Patents are absurd... it results in diametric opposition to the original purpose of patent law, which was to encourage diversity in methods of accomplishing the same tasks.