We all know that some musicians are really influenced by some other musicians (oh here we go again..) which affects their writing / composing style. But what if a song REALLY sounds like another song? I found it difficult to judge whether its just an influence or plagiarism.
So i did some research on the internet and I found some information about plagiarism: The claim against the publisher of the song, which was co-written by Jeffrey Bass and Eminem, was brought by the writer of the 1960s hit “Daydream" performed by The Wallace Collection. The allegation was based on eight bars of a melody used in "Daydream" and in the refrain of "Cleanin’ Out My Closet".
So if a song has exactly the same chord progression, melody, harmonics as the other song for 8 (eight) bars, then it will be considered as plagiarism. source >