Most music uses some basic rules and structures; you can’t just play any group of notes, call it a chord, and sound good. Chords are built on specific note relationships called intervals.
The smallest distance between two keys is called a half step (also called a minor second interval). Two half steps are called a whole step (also called a major second). Any further than a whole step and you stop calling them steps and only call them intervals.
When an interval is called major, it corresponds to the notes from the major scale of the lower, or root, tone. When it’s called minor, it’s lowered by a half step from the major interval.
The term flat or flatted is also used to mean lowered by a half step (flat 5 is commonly used), and sharp/raised indicates the interval moved up a half step (raised or sharp 5 is common). The term perfect is used for the most open-sounding intervals — ones that sound very pure and at rest.
All basic chords are built on three notes: the root (the name of the chord), the third, and the fifth. These names come from the note’s step location in the scale of the same name (the third note of the scale, the fifth note of the scale, and so on).
You can also think of these terms as the interval relationship between the root and the other chord tone. The third is a third higher than the root, the fifth is a fifth higher than the root.
The different chord structures are referred to as chord qualities. This terminology means that for any given note, various chord types can be built on that root tone, and each has a different sound.
The major chord
The most common chord used in music is the major triad. (Triad just means three-note chord.) The major triad has a root, a second tone that’s a major third higher (four half steps), and then another tone that’s a perfect fifth higher (seven half steps) than the root.
Another way to look at it is as a major third interval (four half steps) with another minor third interval (three half steps) stacked on top of it.
Chords are often shown on music notation as symbols above the staff. The major chord is commonly written as just the root note letter (such as C) but may also be written as CM, CMaj, or Cmaj.
The minor chord
If you take a major chord and lower the middle note by a half step, you get a minor chord. A minor chord has a root tone, a second tone a minor third higher, and a third tone a fifth higher from the root.
In other words, it’s a root, a minor third interval (three half steps), and a major third interval (four half steps).
Listen to this track to hear the minor chord.
You typically write the minor chord as the root note’s letter with a small m after it (Cm), but you can also write it as C– (this second notation mostly appears in jazz charts and books).
The diminished chord
A diminished chord is a major chord whose middle and top notes are each a half step lower. It has a root tone, a second tone a minor third higher, and a third tone a flatted fifth higher from the root. You can also think of it as a root, a minor third interval (three half steps), and another minor third interval (three half steps).
You can write the diminished chord as the root note letter with a small circle after it (C”) or as Cdim.
Click here for a demonstration of the diminished chord.
The augmented chord
If you raise the top note of a major chord by a half step, you get an augmented chord (also called a sharp five chord). It has a root tone, a second tone a major third higher, and a third tone a raised fifth higher from the root. That’s a root, a major third interval (four half steps), and another major third interval (four half steps) on top of it.
The augmented chord is written as C+ (because the fifth is raised by a half step) or Caug.
Listen to the augmented chord.
The suspended chords: Sus2 and sus4
The sus chord or suspended chord means that the third of the major triad is suspended or delayed for a bit. It has become very popular today.
The sus4 chord is most common. It has a root tone, a second tone a perfect fourth higher, and a third tone a fifth higher from the root. That’s a root, a perfect fourth interval (five half steps), and a major second interval (two half steps).
The more-modern sus2 chord has a root tone, a second tone a whole step (major second) higher, and a third tone a fifth higher from the root. In other words, it’s a root, a major second interval (two half steps), and a perfect fourth interval (five half steps) stacked on top of it.
The sus chord is commonly written as the root note letter followed by sus4 or sus2, with or without parentheses. If music just shows the note and sus (as in Csus), it means the sus4 version.
These chords have a very open, floating character; many musicians use sus chords for their nice colorful quality.