There's no perfect explanation so it's useful to know a few analogies and ways to explain the problem and choose your explanation based on your situation.
Richard Stallman has frequently mentioned this analogy in parts of his speeches:
With each step, probably nothing happens, but you have to take so many steps, there's no chance of getting across the minefield without stepping on one.
This analogy omits one aspect: when you step on a mine, the damage is instant. When you violate a patent, the patent holder may be aware and might threaten you immediately, or they might decide to let you continue to build your project on that idea and then threaten you later, or they might not be aware now but they will threaten you later when they become aware. This happens most consequently regarding standards. In this way, even if you get across the minefield, you still don't have certainty that you won't get blown up.
A comparison by Richard Stallman (with Gérald Sédrati-Dinet) on how easy it would have been for any of a number of patents to have destroyed great literary works (such as Les Misérables) much in the same way they are threatening and destroying software. Patents cover ideas so pre-empt fixed expressions.
Timothy B. Lee, of The Cato Institute:
In the 21st century, the idea of storyline patents has become a possible problem - but no patent office has yet granted any.
When using this analogy, it's important to keep the ideas of books and plots separate. Literary patents wouldn't cover a specific book - a book is an expression of the idea (covered by copyright). What a literary patent would cover is a part of the plot (which could be used in many books).
Software is not unlike music. Writing software or music is a purely intellectual process, though both require some kind of machine to lend them expression. In both fields, very few individuals ever come up with totally original ideas, yet every composer or programmer has minor new ideas every day. In both fields, the ideas are highly abstract: how would one describe the idea of taking a musical theme and writing variations on it in patent lawyers' language? In both fields, independent invention without copying is not only a theoretical possibility, it happens frequently. In both fields, the test of what is "obvious" is completely subjective. Music, fortunately, is not troubled by patents. But this does not seem to have prevented composers from innovating.
By Chris Lale, January 2003:
Again citing Richard Stallman:
- http://news.zdnet.com/2100-3513_22-121749.html (2nd last section, "If symphonies were patented")
The closing scene of the film Patent Absurdity gives a comical example of a symphony with ideas being removed to avoid patents.
 Richard Stallman quote
For instance, using a particular sequence of notes as a motif could be patented, or a chord progression could be patented, or a rhythmic pattern could be patented, or using certain instruments by themselves could be patented, or a format of repetitions in a movement could be patented. Any sort of musical idea that could be described in words would have been patentable.
Now imagine that it's 1800 and you're Beethoven, and you want to write a symphony. You're going to find it's much harder to write a symphony you don't get sued for than to write one that sounds good, because you have to thread your way around all the patents that exist. If you complained about this, the patent holders would say, “Oh, Beethoven, you're just jealous because we had these ideas first. Why don't you go and think of some ideas of your own?”
Now Beethoven had ideas of his own. The reason he's considered a great composer is because of all of the new ideas that he had, and he actually used. And he knew how to use them in such a way that they would work, which was to combine them with lots of well-known ideas. He could put a few new ideas into a composition together with a lot of old and uncontroversial ideas. And the result was a piece that was controversial, but not so much so that people couldn't get used to it.
To us, Beethoven's music doesn't sound controversial; I'm told it was, when it was new. But because he combined his new ideas with a lot of known ideas, he was able to give people a chance to stretch a certain amount. And they could, which is why to us those ideas sound just fine. But nobody, not even a Beethoven, is such a genius that he could reinvent music from zero, not using any of the well-known ideas, and make something that people would want to listen to. And nobody is such a genius he could reinvent computing from zero, not using any of the well-known ideas, and make something that people want to use.
 A "piano player" music reader
From the ruling on in re Alappat:
As the player piano playing new music is not the stuff of patent law, neither is the mathematics that is Alappat’s “rasterizer.”
An explanation of why a computer running new software is not a "new machine", just as a mechanical piano player playing new music isn't.
- (See also: Computer plus software as new machine)
 Toll booths on roads
Ciarán O'Riordan's explanation of how "software patents are like toll booths, at best, and road blocks, at worst":
 Inequitable Land Grab
Software patents enable early birds to seize ownership over vast (broad) intellectual land needed by many other inventors that come afterward. Like a land grab, the ownership doesn't come from putting in a lot of work but essentially simply for being the first to spot an area and meet minimally complex hurdles. It's inequitable because the land can cover so much area and impact many other very creative folks to come afterward.
 Overlapping Ownership
- (Main article: The notice problem)
Now imagine the land grab example but where more and more claims are allowed to be made to overlapping plots as long as each claim is for a uniquely shaped plot? For software, where development is fast and furious because software is writing and not manufacturing, this adds lots of friction, uncertainty, costs, and injunctions that can lead to bankruptcy.
 Unmanageable Record Keeping
Imagine further that the land grab with overlapping ownership happens so fast that existing records are not searched carefully before granting new deeds? A new deed is frequently given to those who weren't first or to more than one group simultaneously. Most people sued after making investments in a modest plot of land had no idea that land was taken, frequently by multiple parties, and no manageable way to search.
 Lopsided Empowerment
Continuing with the land grab running analogy, most inventions are never patented because those busy creating interesting and challenging things have little time and sometimes money to spend properly applying for claims. It's also antithetical to the spirit of open science and collaboration practiced by so many in the field of software development.
 Related pages on en.swpat.org
- Workspace: A house that computes (analogy) - can this be developed into a useful, succinct analogy?
- Software does not make a computer a new machine#Analogies
- Patents on CII's and pure software patents: what's in a name?, Jonas Maebe - discusses washing machines and mobile phones
- Piano roll blues, Wikipedia
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