I am trying to determinate in which key a song was written. I am not musician nor music student. I knew some clues for finding the key but I am having trouble with a specific song because the criteria that I have used previously contradict each others.
- In the verse the chords are: Bb and Eb. It starts with Bb and uses it most of time: This leads me to perceive Bb as rest and suggest a progression I(Bb) IV(Eb).
- The bridge includes Ab and Bb, which clearly suggests that it is really I(Eb) IV(Ab) V(Bb) as those grades are very common. Also, think "I feel" Ab as IV (but I am very doubtful about that).
- The chorus uses: F, Dm, Bb and Gm. As neither F major chord nor Dm belong to the Eb major key the latter is not the key of the song. Those chords fit well in the key of Bb, but not the Ab major of the verse.
I think that a way of interpret this is as a tonality change from Eb major to Bb major. Is that reasonable? If not, which mistakes I made and how to approach the problem?
Edit: Also F works for the chords of the chorus. Although they share those chords they differ in the use of E and Eb. I found that E sounds better with the music, so maybe it changes from Eb major to F major keys. I've seen many times 1 tone change (in tonality) so maybe it is more reasonable.