Audio: chord (0:16)

Figure: chord
2Interval (Dyad)
Tone cluster
4Dominant seventh
Major and minor seventh
Other seventh
Table: chord

chord plays two part harmony on a theorbo, a type of large lute, followed by four part harmony on a pipe organ. The chord figure, the score, shows that the melody consists of three notes, F-E-E, lasts for two bars, and is repeated four times, each time with a different harmony. The chord table lists the name of every chord covered in the guide together with the number of notes it contains.

A chord consists of two or more simultaneous and different notes.

The word, chord, arose historically from a misspelling of the word, cord, which was short for accord. Accord means something that is in agreement and can be interpreted in one of two ways, as something that is agreeable or pleasant, which is addressed in this chapter, or as something that is coherent or logical or structured, which is covered in the chapter on chord construction.

There is already a word for something that is agreeable or pleasing in music, it is consonance. A consonant sound is agreeable, a dissonant sound is displeasing. Can we define consonance and dissonance in relation to a chord? Well, yes, it has already been done, in contrapuntal consonance.

In counterpoint, intervals are classed as consonant or dissonant. The consonant intervals are unison, octave, third, fifth and sixth. The dissonant intervals are second, fourth, seventh and tritone. A chord is agreeable if it contains consonances and, presumably, displeasing if it contains dissonances. Applying this to chord we note that bars 1, 2, 4, 5, 6 and 8 contain consonant chords, and bars 3 and 7 contain dissonant chords.

This treatment of a chord as a consonant or dissonant entity has three very interesting consequences.

First, an interval is a chord. Since an interval can be classed as consonant or dissonant then it can be treated as a chord. It is useful to distinguish between two notes that form an interval and two notes that form a chord. The term, interval, describes the frequency ratio between two notes, whereas the term, dyad, describes a chord with two notes (a power chord is an example of a dyad). Dyad, however, is not a term widely used in music circles, so interval will often be used instead in the guide, and the context should make it clear whether it means a frequency ratio or a chord with two notes.

Second, there are only two chords with three notes that are consonant. These two chords are the major chord and the minor chord. The C major chord, CEG, shown in bar 8 of chord, contains the intervals, CE, a major third, EG, a minor third, and CG, a perfect fifth. All these intervals are consonant. The A minor chord, ACE, shown in bar 6, contains the intervals, AC, a minor third, CE, a major third, and AE, a perfect fifth. It also contains a doubled note A. Again, these are all consonant intervals. No other chord with three notes is consonant. It is impossible to arrange three different notes to form consonant intervals except in the case of the major and minor chords. This is the reason a chord is sometimes defined as requiring a minimum of three notes, and not two, to be unambiguously identified as a major or minor chord.

Finally, all chords with four or more different notes are dissonant. All of them.

All the features above are demonstrated in chord. The first bar starts with a consonance, DF, a minor third. Adding another third creates the consonant chord, DFA, the chord of D minor, shown in bar 5. Bar 3 starts with a dissonance, BF, a diminished fifth or tritone. Inserting a third between these two notes creates the dissonant chord, BDF, the chord of B diminished, shown in bar 7. An interval of a third can be inverted to obtain another consonant interval, a sixth, shown in the first bar, GE. Rearranging the notes and adding another third creates the consonant chord EGB, the chord of E minor, shown in bar 5. The dissonance, FE, a major seventh, shown in bar 3, can be expanded by inserting two consecutive thirds to create the dissonant F major seventh chord, FACE, shown in bar 7.

The treatment of a chord as consonant and dissonant provides a simple framework for writing chordal harmony: write consonant chords for a consonant sound and dissonant chords for contrast. Write major and minor thirds and sixths together with perfect fifths in two part harmony to guarantee consonant harmony. Write any other interval to guarantee a contrasting dissonance. In three parts, write major and minor chords for consonance and any other chord for dissonance. All chords in four parts are dissonant.

This list of chords gives a good overview of the scope and flavour of some common and not so common chords used in harmony.