I'm sorry for bringing up another "keys and modes" thread, but after searching for other threads I still have doubts about this:
I was playing Heard it Through the Grapevine (by Marvin Gaye)
and noticed it started with a Eb and had both a 3rd minor and a major 6th (3rd and 6th of the Eb). The first thing I though is : "It must be a Dorian/Doric mode", and this led me to think that the song was in C# major, since the Dorian is the second relative to that major scale.
I searched on the internet and I found a different answer though: the song is in Eb major (or so says google). I can't really understand why and I'm kind of frustrated, but since I started studying modes not too long ago it is very likely that I'm missing something here.
Thank you in advance!
EDIT : "Massive" typo, I meant Eb, not Bb