hey, welcome to 12tone building blocks, our monthly series about the fundamentals of music
theory!
last time we talked about secondary dominants, but the comments on that video implied that
I may not have been as clear as I wanted to and since it's a really important topic, I
figured I'd take another shot.
so let's start with some definitions: a primary dominant is a chord that uses instability
in order to point the listener back to the root of the key.
a secondary dominant is a chord that uses instability to point… anywhere else.
this can be hard to visualize so let's try an example.
here's a progression in A major: (bang) the E7 at the end is a primary dominant, because
it points you back to A. the F#7 is a bit harder to explain, but if you listen to it
(bang) it seems to resolve to the B minor.
but that's not the root so how does it work? well, it all relies on a couple properties
of the dominant 7th chord.
for starters, there's only one in each key: while the existence of minor muddles this
a bit, every major key has exactly one dominant 7 chord, built on its fifth degree.
this is the most common primary dominant chord, and our ears have learned to associate each
one with its specific target: for instance, E7 is unique to A major, so even if we weren't
playing in that key, it'd still point us there.
for this reason, we tend to talk about secondary dominants not in relation to the real key,
but as the V chord of its intended target.
that gives us our first clue about what the F#7 is doing.
but in order to really understand it, we have to look at how primary dominant function works,
so let's go back to our E7.
the resolution to A is driven by two notes: the G#, and the D. G# is what's called the
leading tone: it sits a half-step below the root, and it really wants to resolve upward.
it carries a lot of tension, and releasing that tension by moving to the A helps create
that sense of finality and rest.
this is aided by the 4th degree of the scale, in this case D, which sits a half-step above
the 3rd and wants to resolve downward.
that all seems pretty straightforward, but it doesn't really apply to secondary dominants.
after all, if the tension is all based on their position in the key, then where does
it come from when we're not in that key?
in the case of our F#7, we've got an A# and an E, which behave completely differently
in the key of A, so how can they still point us anywhere?
well, that's why it's important that we're using both notes.
here, listen to them together: (bang) yikes.
the interval between these two is called a tritone, and it's generally considered the
most unstable interval of all.
this is where the tension really comes from: not from either note on its own, but from
both of them put together.
every dominant 7th chord has a tritone in it, which means that, without even considering
its place in the key, it already wants to resolve.
from there it's easy enough to figure out where it's pointing because, again, each key
only has one.
usually.
we'll talk about the exceptions in another video.
for now, though, there's one last thing I want to cover.
if you watched our video on chord functions, you know that dominant function is just one
of jobs a chord can have.
there's also tonic chords, which are at rest, and subdominant chords, which act as a bridge
between the other two.
can we have secondary versions of those?
well, you could argue that whenever you resolve a secondary dominant, you create a secondary
tonic.
that is, even if the chord has some other function in the actual key, resolving to it
creates a feeling of momentary rest, called tonicization, which in addition to being an
important effect is also pretty fun to say.
secondary subdominants, though, are a little trickier.
subdominant chords set up the dominants, which means they come first.
when you hear them, they may just sound like normal chords from the key (bang) or they
may not make any sense at all, (bang) but in both those examples the chord right before
the secondary dominant is probably best viewed not in relation to the key but to the target
chord.
just like our secondary dominants are really V chords borrowed from another key, these
are II chords, which have subdominant function, so placing them before a secondary dominant
creates a classic device called a II-V, which serves as almost a fundamental unit of jazz
harmony.
you don't need to set up a secondary dominant with a subdominant chord, just like you don't
need them for primary dominants either, but it adds a little extra strength to the resolution.
anyway, sorry about covering the same topic twice: I don't really like repeating myself,
but this is such an important idea and I wanted to make sure I did it right.
hopefully this time was a little clearer.
either way, thanks for watching!
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