Which Key is this song in? It is in TWO Keys!

[Sethroph]

I listen to a song that uses these main chords:
Bm - G - D - A

I have heard that the key of a piece is NORMALLY, but not always the first chord, so Bm.
But! That is not always the case and I have used a few websites with chord charts and they tell me
that it could EITHER be in the key of D or Bm!? So which one is it? And how do I find out for other songs?
Because I have found this to be quite common with a lot of songs, these websites tell me it is one of two
keys! Which one!? It is very frustrating! I understand if the song is ambiguous (E.g. Electric Counterpoint - Steve Reich)
but I know that these songs are NOT ambiguous!
Can someone explain in a simple way, I'm only 15. Thankyou:biggrin1:

[ToniSteele]

First, you really need to have a good understanding of what major and minor scales are. Once you know that, you can more easily understand chords. Then, you should study basic chord progressions for each key, which are based on scales.

I remember sitting up nights reading a lot of material trying to learn how to read a song, and find out which key a song is in, so that I might easily know which notes to base a solo on. But I haven't found any good guides that sums it all up, just some guides that seem to include some of the material. So I thought I would write a lesson just for getting the basics down. I am a beginner myself(played guitar for just over a year now, and banjo for 2 months), i even tried some online mixing services and love playing guitar so this has become a passion for me. let's take a song called "Me and Bobby McGee." The version I play uses the chords G, C and D. Therefore, this song is in G. Now, why is the song in G? because it had G, C and D in it. consider this chart:
key 1 2 3 4 5 6 7
C C Dm Em F G Am B-dim
D D Em F#m G A Bm C#-dim
E E F#m G#m A B C#m D#-dim
F F Gm Am Bb C Dm E-dim
G G Am Bm C D Em F#-dim
A A Bm C#m D E F#m G#-dim
B B C#m D#m E F# G#m A#-dim
Well for starters, 1, 4 and 5 are ALWAYS Major chords (G, C, F# etc). 2, 3 and 6 are always minors (Dm, Am, C#m etc) and 7s are diminished chords, even though sometimes used as a major in certain songs.
hope you found it helpful

[Sethroph]

First, you really need to have a good understanding of what major and minor scales are. Once you know that, you can more easily understand chords. Then, you should study basic chord progressions for each key, which are based on scales.

I remember sitting up nights reading a lot of material trying to learn how to read a song, and find out which key a song is in, so that I might easily know which notes to base a solo on. But I haven't found any good guides that sums it all up, just some guides that seem to include some of the material. So I thought I would write a lesson just for getting the basics down. I am a beginner myself(played guitar for just over a year now, and banjo for 2 months), i even tried some online mixing services and love playing guitar so this has become a passion for me. let's take a song called "Me and Bobby McGee." The version I play uses the chords G, C and D. Therefore, this song is in G. Now, why is the song in G? because it had G, C and D in it. consider this chart:
key 1 2 3 4 5 6 7
C C Dm Em F G Am B-dim
D D Em F#m G A Bm C#-dim
E E F#m G#m A B C#m D#-dim
F F Gm Am Bb C Dm E-dim
G G Am Bm C D Em F#-dim
A A Bm C#m D E F#m G#-dim
B B C#m D#m E F# G#m A#-dim
Well for starters, 1, 4 and 5 are ALWAYS Major chords (G, C, F# etc). 2, 3 and 6 are always minors (Dm, Am, C#m etc) and 7s are diminished chords, even though sometimes used as a major in certain songs.
hope you found it helpful

Thanks! It is more clear now, and I will do some more research on the topic!