It has to be prety basic but I never understood how it is conventionally explained.
Usually a pop song has a fixed key like in:
Bridge: Am-G, Am-G
How is this analysed?
1) Cmajor song, C root always
2) Cmajor song, C root, then A root in eolian, then F root in lydian mode?
I mean, when Bridge comes, is that a VIm-V or a new Im-V after a key change?
I guess my mistake is that C root and C key does not mean the same