Chord Construction - Triads


One of the most mysterious things when you first start studying music is the subject of how chords are built and which chords can be used where. Thankfully, this is actually a lot more straight forward than you might think. There is a bit of scale theory behind all of this, but for this page I've tried to simplify things a little more - there should be a more exhaustive explanation on another page at a later date.

We'll start by looking at the harmony of the C major scale. This is a good starting point because there are no accented notes (no sharps or flats) so it's a little easier to follow what's happening. Also, we'll stick to simple 3 note chords (called triads) for the time being.

To start with, let's look at the notes contained in the C major scale. These are C, D, E, F, G, A and B.

Music theory says that in a key there are chords built on each degree of the parent scale (you can think of the C major scale as being the parent scale of the key C major). That means that for our example with triads, we will have 7 triads, each one having a different note (from C to B) as it's root note.

When building chords, the process is to start on a root note, and then take notes from the parent scale that are a third above each other. This could be a major, minor or other type of third, but don't worry about that for the time being - it equates to taking alternate notes from the parent scale. For our first triad, we can start on C, and then take alternate notes from the C major scale (E and G) - these are the three notes which form the C major triad.

This process can be repeated using the other notes of the C major scale as root notes, and building on these with alternate notes from C major (the parent major scale). When this has been done for all the scalar degrees, we have a set of seven triads:

Notice that there are three different types of triad here. The 1st, 4th and 5th degrees of C major have major triads (where there is no other symbol, the triad is assumed to be major). The 2nd, 3rd and 6th degree traids are minor (denoted by the 'm' after the triad name, and the triad on the 7th degree is marked with a 'o' symbol (meaning 'diminished'). The reason for these different triad types is because of the intervals contained between the notes in them. To keep these triads in harmony with the parent major scale, we have to use only notes that belong to that scale - but look at the intervals between the notes in the triads:

Triad Notes Interval 1 3 Interval 1 5
C C, E, G Major third Perfect Fifth
Dm D, F, A Minor third Perfect Fifth
Em E, G, B Minor third Perfect Fifth
F F, A, C Major third Perfect Fifth
G G, B, D Major third Perfect Fifth
Am A, C, E Minor third Perfect Fifth
Bo B, D, F Minor third Dimished fifth

The 'major' triads are so called because of the interval of a major third (4 semitones) between the 1st and third degrees of the triad. The name of the 'minor' triads comes from the minor third (3 semitones) between the 1st and 3rd degrees. The diminshed triad also has a minor third between the 1st and 3rd degrees, but it is unique in having an interval of a diminished fifth between the 1st and 5th degrees.

Also notice how on the stave diagram, the chords are 'numbered' using roman numerals. The major triads are marked in upper case, and the minor traids are marked in lower case. A 'dimished' symbol is used to denote the dimished chord, but it is numbered in lower case because of its minor third.

Each of these three chord types has its own distinctive sound - despite their higher or lower 'voices' the three major chords all have a common sort of sound in comparison to the other chord types. Likewise, the three minor chords have their own distinctive sounds. Most people think that the major chord is a 'happier' sound than the minor. The diminshed sounds altogether different because of the very dissonant (unresolved-sounding) interval of a dimished fifth.

This pattern (I, IV, V major chords, ii, iii, vi minor and viio is common to all major keys). As an exercise try harmonising the G major scale in triads and see what you come out with (as a starting point, the notes of G major are G, A, B, C, D, E and F#).

When you know what chords are present in a key, you can build sequences of chords (progressions), and build a melody line over the top of them. The important thing to remember is that you're only using notes that belong to the key (actually you can sometimes use 'outside' notes, but just ignore that for now).

There is a lot more to chord theory than this - all we've really done here is scratch the surface. There'll be more in some other pages (when I get around to publishing them) but hopefully this should show that chord construction is not the black art that it seems to be at first.

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