In 1972, John Fogerty left Creedence Clearwater Revival and their label, Fantasy Records. After he released his hit solo album Centerfield (1985), label head Saul Zaentz of Fantasy Records sued Fogerty for plagiarizing himself. Zaentz claimed that the single “The Old Man Down the Road” infringed upon “Run Through the Jungle,” a song that he had originally recorded with CCR under contract with Fantasy Records in 1970. Though he was not found guilty, it’s pretty novel that Fogerty was sued for sounding too much like himself!
A fifth in 12-TET is defined as seven semitones. Instead of multiplying your frequency by 3/2, you multiply by the 12th root of two seven times, which is about 1.498. That’s close, but not quite on the nose. Major thirds are worse in 12-TET. Instead of multiplying your frequency by 5/4, you multiply by the 12th root of two four times. That gives you 1.25992, which is not very close to 5/4 at all. Nevertheless, we as a civilization have collectively decided that we should just suck it up and live with everything sounding a little wrong. There are plenty of good reasons to!