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Say my target chord is D major or D minor in two separate keys. For example let's say D major is in the key of G major (the V chord) and let's say the D minor is in the key of F major (the vi chord).
Do they both have the same secondary dominant (A7)? the V7/V in the key of G is the same as the V7/vi in key of F? In other words, when I'm trying to figure out a secondary dominant, the V7 of a minor scale is just like V7 of a major scale, provided they share the same tonic (in this example D).
In whatever key, the dominant of D major is A, or A7. In whatever key, the dominant of D minor is A, or A7. The key doesn't influence the secondary dominant. Since there needs to be that leading note (here, C♯) leading to the root D, it applies to both major and minor.
Thus V(7) of V is A(7)>D. Assuming the key of G. Note that a secondary dominant is not always the dominant of the dominant. It could be the dominant of another diatonic chord. If the key is C, then it's V(7) of ii, or, V(7) of II (which is chromatic). Or, in key F, A would be a secondary dominant leading to the vi, diatonically Dm. If, in key C, we're talking about an A chord, some might even call it V of V of V,(V/V/V) but that gets complex.
Say my target chord is Dmajor or Dminor in some random scale. Is it safe to say they will both have A7 as their secondary dominant?
No. The dominant is the fifth scale degree, so A7 is the dominant seventh of both D major and D minor (using the harmonic or melodic minor scale).
The secondary dominant is the dominant of the dominant. That would be an E7 chord.
EDIT: I realized you may have some confusion over terminology. A7 will be the dominant of either D or Dm, but if you're in some other key the same A7 chord will be called a secondary dominant relative to the key.
If you're in C, A7 will be the V/ii; if you're in Bb A7 will be the V/iii, etc. But if you're in D or Dm, A7 is simply the dominant, and E7 is the secondary dominant.
Do they both have the same secondary dominant (A7)? the V7/V in key of G is the same as the V7/vi in key of F? In other words, when I'm trying to figure out a secondary dominant, the V7 of a minor scale is just like V7 of a major scale, provided they share the same tonic (in this example D).
A7 will be the dominant of your goal chord D / dm. The secondary dominant would be E7.
This implies that the dominants of all relative chords (major or minor chords with identical root) are the same.
this implies that the secondary dominants of all relative chords (major or minorchords with identical root) are the same, following the circle of fifths.
No... but yes.
Let me explain...
If you take that major scale, the 5th degree's chord will always be a major triad.
However, the minor scale is more complicated. Since there's 3 of them (harmonic, melodic and natural) you can use all of them to create triads. And even though when it comes to chords, the harmonic minor is the one which is the most used (the name gives you some hint there).
So in a natural minor scale, you'll get a minor 5th degree triad, while in both others you'll get a major one. This means you can actually choose whichever you prefer as your dominant.
Then you get to secondary dominants. To simplify things, let's take your example, in D minor.
So if you chose as your dominant a major chord (A7) then you get back to dominants of major chords which are always major. So you'll get as secondary dominant E7.
Now, if you chose Amin as your primary dominant then you could also choose as secondary dominant a minor chord. You could have Emin as secondary dominant.
And this keeps going. It means you could have something like this:
C#7 --------- F#min --------- Bmin --------- Emin --------- Amin --------- Dmin
V7/Vmin -- Vmin/Vmin -- Vmin/Vmin -- Vmin/Vmin ---- Vmin ----------- I
Okay, this would probably sound like shit but it would syntaxically by perfect.
Another interesting thing is about 9ths because in a minor scale, the 5th degree could be either 9 (melodic minor) or b9 (harmonic minor). While in Major, you'll never get a 5th degree with a b9.
So to summarize:
In D Major, your dominant will always be A, A7, or A9, and thus your secondary dominant will always be E, E7 or E9.
In D minor, your dominant could be A, A7, A9, but also A7(b9) and Amin. Your secondary dominant could be:
And of course, that's if you omit 11th and 13th, 6th and suspended chords, and much more. P.S. It's fun to realise that your forth degree in melodic minor (ascending. Oh... I forgot about ascending and descending melodic minor! Even more fun!) is actually a dominant 7 chord. It's however rarely used. I've only seen it once in Gluck's Orfeo, act II, number 18, maestoso, measure 4.
A Dominant (or secondary dominant) is always a fifth above your "key of the moment" and it's a major chord with minor 7. So yes it doesn't matter what chord quality you are looking at, it will always be the exact same chord.
Well to clear up a little misconception here, a lot of people say a dominant could be e.g.g. A or A7 but this is only to a small percentage true. It is true that you call the fifth chord of a major scale dominant (when leaving the minor7 out) when thinking of the Roman numeral theory or functional analysis. However, it is in deeper conceptual analysis a statement about the quality of a chord. So to represent a true dominant, quality-wise, you have to play a minor7 over a major chord. You need the tritone intervall in your dominant chord to make it truly dominant. The tritone is in this case the intervall between major3 and minor7. This is also the reason why some people call the 7th chord in a major scale, the half diminished chord, a shortened or rootles dominant.
To take it a step further, now we know it is the tritone. Turns out that always two chords share the same tritone intervall and you can substitute them. This is called tritone substitution. You can basically always substitute your dominant for the dominant a tritone(6 half tones) away from it, as both contain the same tritone intervall and resolve to the same target chords. This sounds complex at first but it is really easy and once you know of it you should be able to easily identify it in chord progressions. Many times it's used in a 2-5-1 to create a chromatic run. For example dm G7 C becomes dm Db7 C. You can find this for example in Bill Evans "Alice in wonderland".
Sorry if I went a bit off topic here but I feel it is still within the boundaries of Dominants.
