[aeon_ai]

This is one of those fun "achsully" responses I get the privilege to refute.

It's a foundational principle of copyright law, codified in 17 U.S.C. § 102(b): "In no case does copyright protection for an original work of authorship extend to any idea, procedure, process, system, method of operation, concept, principle, or discovery"

Now, we can quibble over what qualifies there, but the dichotomy itself is pretty clear.

This goes back to Baker v. Selden (1879) and remains bedrock copyright doctrine.

The Tetris case is overstated. Tetris v. Xio did not establish that The Tetris Company "owns the idea of falling-tetromino puzzle video games." The court explicitly applied the idea-expression dichotomy and found Xio copied specific expressive choices (exact dimensions, specific visual style, particular piece colors). Many Tetris-like games exist legally, and it is the specific expressive elements that were considered in the Xio case.

K.C. Munchkin is old and criticized. That 1982 ruling predates major developments like Computer Associates v. Altai, which established more rigorous methods for filtering out unprotectable elements. The Munchkin decision continues to be debated.

"Substantial similarity" analysis itself incorporates idea-expression filtering. Courts use tests specifically designed to separate protectable expression from unprotectable ideas, especially when considering the four factors of fair use (when applied as a defense.)