Welcome back to "Continuous Hit Music" as we continue uncovering the inner workings of music. In the last installment, we started taking a look at chords and the three primary chords in a key; this time around, we're going to look at the relation between two of those chords.
Give a listen to this chord:
How do you feel after listening to that? If you're like me, you're a little on-edge; you're waiting for the next chord. I know there's a next chord, and it's not coming. I'm getting exceedingly impatient. But it's not coming.
Well, not on that sound clip. Here's that chord, with its resolution:
If you didn't inherently feel the tension listening to the chord on its own, you probably at least felt that the second chord was the logical place to go. Now it feels like we can move on; if we're just left hanging on that first chord, we need it to finish. But why? What makes that chord "need" to resolve?
That chord draws you to another chord so strongly because it is a dominant seventh chord. In the key of C, that's a chord made of the notes G, B, D, and F. In the last installment, we built chords out of three notes, made of notes a third apart; this extra note, F, is just another third above D.
The addition of this extra note creates a number of interesting relationships between the notes in the chord and the key that it is in. Let's start by looking at the notes in the key of C:
Notice how there are two places in the key where the next note is a half-step (one key away) rather than a whole-step (two keys away): between E and F, and between B and C. These half-step intervals give the scale a bit of asymmetry that helps us to identify the key. If two notes are heard a half-step away, that gives us an aural clue as to what the key is. Furthermore, we expect each of these half-step relationships to resolve towards the tonic chord (in this case, C major, or the notes C, E, and G). If we hear an F, we expect it to go down to E; and if we hear a B, we expect it to go up to C.
Furthermore, B and F relate to each other in a unique way; they aren't a perfect fifth apart, but instead a "tri-tone." If we were to build a chord out of each individual note in the key, the first note and the third note would be a perfect fifth apart and sound nice and harmonious. The B and the F, however, are a slightly smaller interval, the "tri-tone" or "diminished fifth," which isn't nearly as harmonious. Listen as each scale degree is played with its corresponding fifth, and then listen as the tendency tones resolve in their given direction:
The inclusion of the tri-tone immediately lets you know what key you're in, and the identities of each note in that key lets you know exactly where it's going. Add that into the natural relationship of the G note to C as its most closely related note, and you've got a chord just begging to go to C. This is how many songs settle themselves into a given key; it's also a useful tool for composers to move from key to key. If you're in the key of F, for example, and suddenly there's a G dominant seventh chord, you know you're about to move into the key of C. It's a big sonic red flag that tells you where you're headed.