[raganwald]

Once you start calling anything an invention, the next logical step is to allow to patent it.

“Invention” and “Patent-worthy Discovery” are not synonymous:

  An invention is a better or more effective composition,
  device, or process. An invention may be derived from a
  pre-existing model or idea, or it could be independently
  conceived in which case it may be a radical breakthrough...

  An invention that is novel and not obvious to others
  skilled in the same field may be able to obtain the legal
  protection of a patent.

https://secure.wikimedia.org/wikipedia/en/wiki/Invention

It is possible and normal to invent things that are not novel, or may be obvious to others skilled in the same field. It’s still invention, it just isn’t “Big I” Invention, it’s a more modest creative process.

Think of it this way: We have the expression “re-inventing the wheel.” If it wasn’t possible to invent things that already exist, it wouldn’t be possible to “re-invent” anything, would it?