In this article, I’m expanding on my previous piece, “Why I-IV-V Works, And Works So Well.” I’ll be adding 7ths to the chords and starting to talk about harmony a little more.
The Polarity of Notes
As I discussed in the previous article, harmony is all about tension and release, and certain notes in a given key have certain amounts of pull to one or more other notes to achieve this. The Leading Tone of the key (Ti in solfege) wants to resolve to the Tonic (Do). Your ear gets accustomed to the key you’re in pretty quickly. Once you’ve heard the I chord a couple times, the V chord will naturally pull back to the I. There are two reasons for this:
Adding Tension
When we start extending the chords beyond simple triads, we get more notes with more pull, and thus more tension. This is where “classical” harmonic theory and blues-based theory part ways a little bit, but I’ll attempt to bridge the gap and present both sides of the issue.
Classical Harmony
In the classical harmony you learn in music school, the 7th generally only gets added to the V chord (generally called the Dominant in the classroom). Adding the 7th to the Dominant adds tremendous tension, because it creates the interval of a tritone in the chord. In the illustration below, I’m using the key of C, so the Dominant chord is a G7. The tritone is between the 3rd and 7th of the chord (B to F).
In terms of pull as we’ve discussed, the tritone in root position is a sound relationship where the two notes in the interval pull toward each other. If you invert the chord to put the B above the F, the pull shifts such that the notes now want to push away from each other. The result is the same: B resolves to C, F resolves to E. C-E is all you need to outline a C Major chord, a.k.a the Tonic. This pull from the Dominant to the Tonic is further enhanced by the presence of the Supertonic (also called the 2nd) of the key. Its pull is also back to the Tonic. And the root of the Dominant, being the 5th of the Tonic, lends smoothness to the whole affair.
Blues-based Harmony
When I say “Blues-based,” I’m talking about all Blues music and the majority of Funk music, Soul, Gospel, and even some Jazz. These harmonic practices depart from classical practice in that all the chords used are Dominant chords, with a tritone relationship. Here’s a quick comparison between the I, the IV, and the V chords in both genres.
Definition: Diatonic – all notes belong to a given key, and only that key.
We see here that the chords used in Blues-based Harmony are from different keys. The I would be called the Dominant to the key of F in Classical Harmony. The IV would be the Dominant to the key of B-flat, and the V would be the Dominant to the key of C. This explains why the progression works even when each chord belongs to a different key: the tritone still gets resolved the way it wants to, and still brings the progression back to the Tonic.
If you were to add the 7th to the IV chord (called the Subdominant in Classical Harmony), it would give you a Major Seventh chord (F-A-C-E) versus the Blues-based model where it’s a Dominant chord (F-A-C-Eb).
A final note on Roman numerals: In Classical Harmony, the numerals are used to indicate the quality of the chord. Major chords are indicated with capital letters (I, III, IV, V) while minor chords are indicated with lower-case letters (ii, vi, vii). These are then altered with other symbols to indicate things like a Diminished quality (viio) or a Dominant quality (V7). In Blues-based Harmony, a Dominant quality is assumed, and so the numerals are used without adornment. But, it just so happens that the I, IV, and V are all major chords anyway, so they tend to look the same in both genres.
more articles by Brien Henderson
- Anatomy of the Blues Scale
- A Great Site for Old Music
- Every Musician Should Read This
- Saxes: Work Your Pinkies!, part 1
- Spice Things Up With The Tritone Sub
- Writing Your Own Music: How To Get Started
- Intro to chords in Jazz
