Substantial similarity

The test of substantial similarity (or "probative similarity") is whether, considering the two works as a whole, including both the copyrightable elements and the uncopyrightable ones (such as basic ideas or public domain expressions that are not eligible for copyright), a reasonable person would conclude that the defendant had actually copied the work from the original. This standard focuses on the works' similarities rather than their differences. Thus, "[i]t is enough that substantial parts [of a copyrighted work] were lifted; no plagiarist can excuse the wrong by showing how much of his work he did not pirate."

Note that this test is designed to determine whether copying occurred, not necessarily whether that copying constituted infringement. If the court determines that actual copying has occurred, only then does it assess whether the copying was substantial enough to constitute infringement. Unfortunately, many courts also refer to this test as one of "substantial similarity," which can lead to confusion. To avoid this confusion, many courts prefer to use the term "probative" similarities to show "actual copying," and "substantial similarity" to show "actionable copying." See Positive Black Talk Inc. v. Cash Money Records, Inc., 394 F.3d 357, 370 (5th Cir. 2004); Dam Things from Denmark, 290 F.3d at 562 & n. 19.