Harmonization
of the degrees of the major scale

Harmonization of the three note chords

The construction of a chord means the harmonization of the degrees of a scale. This system, seen in the triads section, has already been used in the works of great composers for centuries, and can be adapted to the modes of the scale. The chord results from overlapping notes and are played simultaneously, that have afinity for themselves. The laws of classical harmony indicate the construction of a third interval chord, that creates four types of triads (major, minor, diminished and aumented). Practice on the construction of the triads which, especially in modern music (of whatever style), are used not only from a harmonic (and therefore chords) level, but also in the exposure of melodic themes and instrumental solos.
The triad is formed by the I°, III° an V° of the scale. This chord is made up of three notes (therefore the term triad) but, as we will see, the harmonization also allows the building of four note chords (quadriad) or more. For now we are only interested in how to harmonize triads of the C major diatonic scale, using modes. We must always keep in mind that, starting from the root, we need to overlap the third interval notes. If you look at the line below, you can verify the procedure. The C note, first degree of the ionian mode of C major, is overlapped by its third, which in this case is E. The interval that comes between the two notes is the third major.
The E note has to be overlapped by its third, remaining in the ionian mode, and obtaining the G. Combining all three notes, forms the triad of C major.

Now we can harmonize the scale of C major, divided into the seven modes that we saw in the previous page. The harmonization system is obviously by thirds, and we will therefore create a three note chord (triad) for every mode of the scale. In the table, you will see (every line is a mode):
- the degree from which the mode is built;
- the line with the notes of the scale and the relative chord;
- the notes of the chord;
- the intervals that characterize the structure of the chord;
- the abbreviations. 

The abbreviations of the major chords are seen in the name of the root note (C = chord of C major), while in a minor chord we find a lower case m next to the name of the root (Dm = chord of D minor). It's also possible to find the wording of the minor chord with the - symbol next to the name of the root. The term dim means diminished, and can also be written as mb5.
You may have noticed that with three note harmonizing of the major scale, you get the following three types of chords:
-  major triad  put in the ionian mode (first degree of the scale), lydian (fourth degree) and mixolydian (fifth degree);
-  minor triad   put in the dorian mode (depending on the degree), phrygian (third degree) and aeolian (sixth degree);
-  diminished triad  put in the locrian mode (seventh degree).

Harmonization of four note chords

It is now necessary to analyze the abreviations of the four note chords, in order to fully understand their harmonic construction. With the addition of the seventh degree to the triad, we now have four types of chords that can be obtained from the modal harmonization of the major scale. In the name of the chord we find the number seven, which indicates the seventh degree.
1) When the seventh is major (in the sense that it creates a seventh major interval with the root), next to the name of the chord the denomination maj7 is added, which is an abbreviation for the term major.
2) When the seventh is minor, which means it creates a seventh minor interval with the root, only the number 7 is added to the name of the chord. In the major scale, the seventh is therefore minor (or flat) for the three m7 chords (dorian, phrygian and aeolian modes), the mixolydian mode (seventh chord), and the m7b5 (locrian mode).

3) Sometimes maj7 is replaced by the symbol .
In the minor chords, it's possible that the letter m can be replaced by min (for example Dmin7) or -7 (for example A-7), even if they both mean the same thing.
In the min7b5 chord, the abreviation can be also the   symbol, which is read half diminished.

We can summarize everything in the table below, where four types of chord are listed that come from the four note harmonization of the major scale. Notice how the most important seventh chord comes from the mixolydian mode: its characteristic is to find itself at the harmonic center of the root (it's possible to have a larger number of harmonizations with this chord), and therefore is dominate with respect to the other types of chords. This is where the term seventh dominant comes from. Here are the four types of seventh: