Explaining DADA to EGBG (and in the other direction) in theoretical terms

Question

Please can you help me describe the transition between these two sets of notes in theoretical terms:

DADA

(For clarity, on the guitar: open D string, g string 2nd fret, b string 3rd fret, e string 5th fret)

EGBG

(Guitar: d string 2nd fret, open g string, open b string, e string 3rd fret)

DADA isn't a chord as only two notes but could be described with as an interval: a perfect fifth (D to A). EGBG could be described as an Em chord (EGB) but that's missing the important high G note.

How do I describe these two sets of notes and transition between them? Does playing these two chords in different orders change the key? (Minor v Major)

Answer 1

Taking D and A notes as a sort of D chord, which could be just about construed as D maj (more chance of hearing an F# harmonic than an F), then the transition between the two could be I>ii, as the other chord is definitely Em.

However, playing the Em first, followed by the D could put things into Em key, as Em and D both emanate from that key.i>VII would be RNs.

So, either scenario works, but adding a 3rd chord would clarify things. With an A(7) chord, it fits firmly into D, whereas with a B(7)it fits firmly into Em.

Incidentally, there is no 'important high note'. As Todd says, three notes such as 1,3,5 will constitute a triad chord, no matter what order, and no matter how many different 1s, 3s and 5s are played. Where did that idea come from?

Answer 2

It's ambiguous. Here are merely some of the diatonic possibilities:

Em: VII i

D: I ii

G: V vi

C: ii iii

Am iv v

The reason why these are the first possibilities is twofold: First, the D-A interval first suggests a D chord. It's literally a D5 chord, which is a D chord but is ambiguous in terms of flavor - major or minor. Depending on context, D-A could be heard as an Asus4 chord, but we don't have any reason to hear that in this case.

The second factor is the E minor chord. That is not ambiguous at all - it's an E minor chord. Since it is a major second away from the likely D chord, it tends to imply the D chord is major, because the only diatonic pair of minor chords a major second apart are ii - iii in a major key or iv v in a minor key, which are less common, but possible.

Since there isn't a firmly established key implied by just these two chords, playing additional chords wouldn't necessarily be heard as a key change. Changing the order in which you play these two chords doesn't do very much at all. It's still ambiguous, you would just reverse the order of all the possible interpretations.