Hey Friend,
In the key of A major, D major is the IV chord in the harmonic progression. Let's do a quick review so we know how far down the path we've gone.
The A major scale is as follows:
A B C# D E F# G# (A)
The resulting chords that come out of that scale and give us the chords we've been studying are:
I IIm IIIm IV V VIm VII° A Bm C#m D E F#M G#°
The IV chord sound helps to relieve some of the tension cause by the IIm and IIIm chords on the way to V chord. In this case, D major is leading up to the V (E) chord, which is roughly in the center of the key.
D major is made up of the D, F# and A notes, so it's the first chord in the key that takes us into the next octave in the scale with the A note. Just an observation, as we don't really spend much thought on individual notes when we're playing chords.
Here are the exercise files for D major again. The intro piece gives you some practice working with open D major, and the positions exercise take you up the guitar neck with various locations and shapes on the neck.
D major has always been one of my favorite chords, probably because it was one of the first chords I learned, and it's pretty easy to play in the beginning. It is heavily used in Rock, Country and Blues, and many songs I know either center around D or have a D major chord in them. For example, for years, the song " More Than a Feeling" by Boston was typically the very first thing my hands would go to every time I picked up a guitar. It was like a go-to song my muscle memory defaulted to as soon as my hands felt the neck. The very first chord in the intro progression is an open D.
Let me know if you have any questions. Rock on!
Peace~
Dave
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