Expression vs Invention: The Dividing Line
Copyright protects original expression (words, music, visual art, software code) fixed in a tangible medium. It does not protect ideas, facts, or methods; it protects how those are expressed. A novel about time travel is copyrightable; the idea of time travel is not. Patent protects new, useful, non-obvious inventions: a chemical compound, a machine, a process, or a design. A patent requires novelty (not previously disclosed), non-obviousness (not a trivial variation of known art), and utility (it must work). Copyright arises automatically when the work is created; patent requires filing and examination by the USPTO. Copyright lasts the author's life plus 70 years; patents last 20 years from the filing date (design patents, 15 years).
What Each System Prevents
Copyright is infringed when someone copies the expression without permission: reproducing the text, adapting the story, translating it, or publicly performing it. The owner can sue for damages and seek injunctions. Patent is infringed when someone makes, uses, or sells the patented invention without a license, even independently. A inventor who unknowingly invents the same thing infringes if a patent is in force. For software, the choice is strategic: code can be copyrighted and/or patented (or kept as trade secret), and companies often pursue multiple layers. Copyright is simpler (no filing required); patent is stronger (prevents independent invention) but costlier and slower.