Harmony is the result of polyphony (more than one note being played simultaneously).
Origin of term
The word harmony comes from the Greek ἁρμονία harmonía meaning 'a fastening or joint'. The concept of harmony dates as far back as Pythagoras. Therefore it is evident why it is used to refer to a connection between people joining in 'peace'.
An interval is the relationship between pitch two separate musical pitches. For example, in the common tune 'Twinkle Twinkle Little Star', the first two notes (the first 'twinkle') and the second two notes (the second 'twinkle') are at the interval of one fifth. What this means is that if the first two notes were the pitch 'C', the second two notes would be the pitch 'G' — five notes, or one fifth, above it.
A table of common intervals:
The combination of notes to make intervals creates harmony. A chord is harmony, for example. In a C chord, there are three notes: C, E, and G. The note 'C' is the root tone, with the notes 'E' and 'G' providing harmony.
In the musical scale, there are twelve pitches. Each pitch is referred to as a 'degree' of the scale. In actuality, there are no names for each degree—there is no real 'C' or 'E♭ ' or 'A'. Nature did not name the pitches. The only inherent quality that these degrees have is their harmonic relationship to each other. The names A, B, C, D, E, F, and G are intransigent. The intervals, however, are not. Here is an example:
No note always corresponds to a certain degree of the scale. The 'root', or first-degree note, can be any of the twelve notes of the scale. All the other notes fall into place. So, when C is the root note, the fourth degree is F. But when D is the root note, the fourth degree is G. While the note names are intransigent, the intervals are not—in layman's terms: a 'fourth' (four-step interval) is always a fourth, no matter what the root note is. Any song can be played or sung in any key—it will be the same song, as long as the intervals are kept the same.
There are certain basic harmonies. A basic chord consists of three notes: the root, the third above the root, and the fifth above the root (which happens to be the minor third above the third above the root). In a C chord, the notes are C, E, and G. In an A-flat chord, the notes are A♭ , C, and E♭ . In many types of music, notably baroque and jazz, basic chords are often augmented with 'tensions'. A tension is a degree of the scale which, in a given key, hits a dissonant interval. The most basic, common example of a tension is a 'seventh' (actually a minor, or flat seventh)—so named because it is the seventh degree of the scale in a given key. While the actual degree is a flat seventh, the nomenclature is simply 'seventh'. In a C7 chord, the notes are C, E, G, and B♭ . Other common dissonant tensions include ninths and elevenths. In jazz, chords can become very complex with several tensions.
Typically, a dissonant chord (chord with a tension) will 'resolve' to a consonant chord.
There are four basic 'parts' in classical music—soprano, alto, tenor, and bass.
There can be more than one example of those parts in a given song, and there are also more parts. These are just the basic ones.
The four parts combine to form a chord:
- Bass – root note of chord (first degree)
- Tenor and Alto – provide harmonies corresponding to the third and fifth degrees of the scale; the Alto line usually sounds a third below the soprano
- Soprano – melody line; usually provides all tensions
Note that it is the most basic and distilled example of four-part harmony. There is a nearly infinite number of alternate harmonic permutations.