Intermediate Music Theory Lesson 1: 7th Chords
Originally posted on February 19, 2010
To it then.
The Importance of the 7th chord
How to construct a 7th chord
First, let’s look at a major scale.
Cmaj scale.mp3 Starting at C, lets extract every other note. We wind up with four notes stacked on top of one another:
This is a C Major 7th chord. It is named this because it consists of the first degree of the scale, the major third, the fifth, and the major seventh. In lead sheet notation you signify it as major by the suffixes seen above (M, maj, ∆) Some other ways to think of it are as two perfect fifths a major third apart or as a major third followed by a minor third followed by a major third. (There are other ways to think of it. How many can you think of?)
The 5 Basic 7th Chords to Know
So, we’ve gone over where the major 7th chord comes from. Now, these next four chords I will explain in terms of the major seventh. In other words, if it says b7, that will signify the flatted 7th of the major 7th chord. In next week’s post we will go over where these chords derive from, but for this week, just being able to recognize them will be a good start.
First is the dominant 7th chord. This chord has a flatted 7th with a natural 3rd and 5th. Its chord symbol is signified by, simply, the number 7. In other words, if you see a chord symbol that is simply X7, it is implied to be dominant. Note the unique interval of a tritone (or b5/#4) between the 3rd and the 7th of the chord. This interval lends the chord its tension with both pitches wanting to move toward the tonic chord (the root major). One other way to think of this chord is as a major third followed by a minor third followed by a minor third.
Next, the minor 7th chord. This chord contains a flatted 3rd and 7th. In lead sheet notation a minor 7th is signified by a lowercase m, or the suffix min7. This chord, like the major 7th chord, is based around perfect 4ths and 5ths. I like to think of the two being related, at least in that sense. (Food for thought: what happens when Cmin7 is played over an Ab in the bass?? If you’re confused by this, don’t worry; either ignore it or file it away) Other ways to think of a minor 7th chord are as two perfect fifths a minor third apart, or a minor third followed by a major third followed by a minor third.
Now we come to the half-diminished chord, or the minor 7th with a b5. As seen above, in lead sheet notation this chord is signified by either a circle with a line through it (∅) or the suffix min7b5. I like to think of this chord as mysterious sounding, but you can certainly make your own judgement call. Note again, the tritone between the root of the chord and the b5. This gives tension to a different part of the chord than a dominant chord, which gives it its unique sound. You can also think of this chord as a minor third followed by a minor third followed by a major third.
This is the fully diminished 7th chord. This chord has a b3, b5, bb7 (yes a double flat 7th! This means that you flat the note once, then you flat it again. Bbb=A). Lead sheet wise it’s either written with a circle (º) or with the suffix dim7. Oh what a tense chord! There are two tritones in this chord offset by a minor third, or all minor thirds stacked on top of one another. You can tell by listening to it that either there’s danger afoot or it should move to a more peaceful (or dissonant!) chord.
These five chords are by no means the ONLY 7th chords to exist. They are just the most basic. If you want to do some exploration, see what it sounds like when you try to flat and sharp different parts of the 5 above chords, not to mention the inversions of all the 7th chords. It simply opens the palette to different sounds, which, in modern composition, is half the name of the game. In the next lesson I will take you through where these 5 chords are derived from (I’ve already started with the Cmaj7 above), and how they function (and in a later post, how they move together), so take care to remember this lesson.