You have to understand, there are a lot of things in play here, there is no simple answer.

As an example, you have “style”. You know, blues, rock, jazz, whatever. Most musical styles have hooks, have phrasing, have beats, whatever that defines they as a style. Often when you write a new song “in a style”, you limit your choices as to what to play, what chord progressions to use, etc.

However, I do think there is a big difference in “playing something in a blues style” and “sampling something in a blues style”. Because even if the results are very similar, only one contains the new players inflections, tonality, and the like.

Sampling is the easy way out too often, it’s more about a sound and less about pure originality. It’s why in the end the line is drawn pretty simple: If you use the performance of someone else, you need permission / license. If you use the song (words and music) written by someone, you need permission / license.

You have to remember too that there are many artists is in the music business who are only performers, they don’t write their own music, they merely perform the songs written by others. In the R&B world, example, there are “producers” who only make beats, or who only make melodies. There are others who only write lyrics. Often a song is made up of beats from one, melody of another, and lyrics from a third, performed by session musicians or by the producers themselves, and combined to make a new song, sung by the “performer”. It is the collaborative nature of modern music that can create it’s own hell.