Episode: 1754
Title: HPR1754: D7? Why Seven?
Source: https://hub.hackerpublicradio.org/ccdn.php?filename=/eps/hpr1754/hpr1754.mp3
Transcribed: 2025-10-18 08:51:42

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This is HPR Episode 1754 entitled B7, Y7.
It is hosted by John Colp and is about 14 minutes long.
The summary is, I explain what 7 chord marks and when to use them.
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Alright, John Colp and Lafayette Louisiana with yet another hacker public radio episode.
I'm on spring break right now so I'm catching up on recording a bunch of topics that I've
been meaning to record.
Today I'm going to address one of the requested topics at hacker public radio and it is a music
theory topic.
Now this is sort of a busman's holiday for me because I am a music professor.
I have a master's degree in music theory and a PhD in musicology and so if I had never
done any episode about music theory it would seem a little bit mean I guess to ignore
my expertise in this when somebody has specifically requested it.
So today I'm going to talk about something that may have been confusing or puzzling to
people in the past.
I know in the hacker community, that's pretty nice there, the hacker community.
There are lots of musicians and lots of people who play the guitar or the piano or whatever.
And so I think this is something that should hit the mark with quite a few people.
I'm going to do the best I can to explain it in ways that just about anybody could understand.
However I will also have a list of the terms that I use in the course of my discussion.
I don't at this point know exactly every term I'm going to use because I'm just going
to wing it.
But I've already put together a list of terms that I think I might use in the course of
the discussion.
The topic is seventh chords and the title of the show is D7 Y7.
And I call it that because people who play the guitar, especially if what they play
is popular music, they probably read from lead sheets and things like that if they want
to play songs or if they're writing out a chord sheet for a song, they're composing
themselves.
They will put things like D, G, C, maybe they'll go into, I don't know, AM for A minor
or EM for E minor.
But there will also be chords with a seven next to them.
So you might see a progression like G, C, D7, G.
And you may have asked yourself, what is the seven?
I mean, I know I put my fingers in a different place and it sounds a little bit different,
but what is the significance of the seven?
So let me play for you the difference between the chord without the seven and the chord
with the seven.
Here's the progression I just mentioned, G, C, and I'll just do D and then G, G, C, D, G.
This is a very standard progression in theoretical terms, it would be 1, 4, 5, 1.
And if you, there's an old joke that if you know those three chords, you can play about
10,000 songs and it's probably pretty true.
So G, C, D, G.
Now sometimes you might see the D change to a D7 and that would make it sound like this.
G, C, D7.
Now you wonder, what is the difference there?
What's the difference between this, D, and this, D7?
Well the difference is one note and it's the seventh.
What happens in a seventh chord is there is an element of dissonance that's introduced.
Dissonance is a relatively unstable sound between two chord members.
Consonance is when the chord members sound stable and good together.
Dissonance is something that is really, really important in Western music because it's
what helps make the music sound a little bit more interesting.
So this chord, the D, doesn't really have any dissonance in it, but this one does have
some dissonance.
If you listen between the root of the chord, that's the D, and then this, these two notes
together, that makes an interval called a seventh and the seventh is a dissonant interval.
Disnant intervals typically need to do what's called resolving.
Now there's another dissonant interval inside this chord also between the seventh and the
third of the chord, the third is F sharp and the seventh is the C. So these two together
sound like this.
This is a dissonant interval, it's an interval called an augmented fourth, and this calls
for a resolution like so, oops, sorry, mess that up.
And so when you play the whole chord, like that.
So the reason somebody would use a seventh chord is to make a stronger pull from one chord
to another.
If I do just the D chord, going to G, it sounds good, it does not sound like it absolutely
must go there though.
This D chord, I could just stay on there indefinitely.
But this chord, with this dissonance between the root and the seventh, that really needs
to resolve.
And it almost always resolves back to the chord a fifth away there.
Now it doesn't have to, it could do what's called a deceptive resolution where it would
do something like this.
And resolve to the sixth instead of the one.
But the normal thing is for it to resolve back to one.
Now the seventh chords are something that, let's take the same progression, G, C, D, and G.
You wouldn't necessarily put a seventh on either the G or the C chords, unless what you're
trying to do is to undermine their sense of stability.
Now moving from G to C, it would be very common to add the seventh.
And you would only add the seventh to the G chord if what you wanted to do next was go
to the C.
There's a G7 chord, and that wants to pull to there.
So you get this interval that resolves here.
Now you would probably not add a seventh to the C chord because it would start pulling
you in a different direction than D. If what you're trying to do is go from C to D, then
you would not add this note.
The B flat, because if you add the B flat there, that starts pulling you towards the F chord,
which is not part of our little progression here.
So anyway, the big picture is that the seventh chord is something that pulls strongly toward
another chord because of the presence of some dissonance.
There was a great song that we used to play in the band I was in in graduate school,
was a band that played Cuban pop music from the 1920s and 30s.
And I guess sometimes from the 40s, but anyway, old Cuban music.
And there was one song that I absolutely loved called Lagrimas Negres, Black Tears.
And that song had some excellent use of seventh chords in it.
It was a song that's in D minor, like this.
And it went, let's see, D minor, to G minor, and then to C major, to F major.
And then back to D minor, G minor.
But the way we played the song, we made a stronger pull from one chord to another by adding
sevens in there.
So instead of just going like this, we would instead go from D minor to D7, that increases
the tension, makes it inevitable to go to this G minor, and then to C, and here we'd add
the seven, to go to F, and then to get back to D minor, I'd do an E7, A7, D minor.
So yeah, it makes for a really nice progression and a strong pull from one chord to another.
Hope you all enjoyed that.
So play yourself some seventh chords on your guitar.
Bye.
