The westerners are accustomed to hearing melodies having a background of harmony. Harmony acts as a third dimension of the movement of the melody. It adds richness and colour to the melody. Harmony to music is what perspective is to painting. It creates meaning. The supporting role of harmony is clearly observed when a singer is accompanied with chords on a guitar or piano. When a pianist plays the melody with his right hand, the melody is made rich with the chord-work with his left hand. If a wrong chord is sounded while playing, the mood or the feeling of the artiste or the listener gets disturbed. This is due to the unity of melody and harmony being broken at that moment.
Harmony gives a shape and volume to the melody in relation to the chord-work. A chord may be defined as the combination of agreeable tones occuring simultaneously at any moment. Just as a roof rests upon columns, melody rests upon supporting chords. Melody is the horizontal aspect of music while the harmony is the vertical aspect. This building which is being constructed by making use of the bricks made of melody and harmony is the conceived picture or the feeling experienced by the listener. This feeling can vary according to the quality or form of the melody and harmony applied.
The chords are the framework of a composition. The chords are the elements of the structure which holds the melody composition together or make it stable. The chords have meanings in relation to other chords. This is similar to the single notes having meanings in relation to other single notes in case of Raga music.
TRIAD / COMMON CHORD
The most common chord in Western music is the Triad. A Triad can be built by combining the first, third, and fifth degrees of the main scale do-re-mi-fa-sol-la-ti-do.
For example do-mi-sol is one triad. The second, fourth and sixth is another triad, e: re-fa-la and so on. The triad is the basic formation in Western music. It is the force of gravity in the propagation of the melody in Western music. This concept is very much similar to the absorption of the artiste at the mail shruti Sa or basic pitch in case of performing oriental or Raga music.
Although the triad is a vertical block of sound, its function in moving the melody is exhibited in a horizontal form, while the relevant harmonies take the vertical positions.
The keys of the piano are named as C, D, E, F, G, A, B, C. Therefore we can build traids such as C-E-G, D-F-A, E-G-B, and so on. These triads from the material in Western music and they impart character and meaning to music.
CONSONANCE AND DISSONANCE
Dissonance arouses the feeling of restlessness or activity while consonance arouses the feeling of relaxation and fulfillment. The dissonant chord creates tension and the consonant resolves it. This concept is frequently used in the creative background of music in dramas and films of the Western world.
To explain this relationship between the consonance and the pleasantness (joy) and also the dissonance and the unpleasantness ( pain). It is useful to observe the numerical ratios formed by the relation of the numerical frequency values of the notes. The most agreeable relation of two notes is found when they exist as the fundamental and the octave position. If we consider the numerical frequency values of the Middle C (S) which is 240cps and the Octave C (S) which is 480cps, we see that their ratio is 1:2. Therefore this ratio 1:2 is the most agreeable ratio of notes when they are sounded together. This ratio of frequencies is known as the musical interval. It is noticed that the ratios 3:2, 4:3, 5:4, etc., also produce pleasant sensations but no so perfect as 2:1. This shows that the blending of notes is better when the ratio as simple. For example, if we sound the two notes C (S) and D (R) together, we will see that they cannot blend together and the dissonant property is very high and is very unpleasant to the ear. Their frequency ratio is 240:270 - that is 8:9 which is not a simple ratio.
PLEASANTNESS OF TRIADS
Through experience we know that the triad or the three notes C (S), E (G) and G (P) are sounded together. The product gives a pleasant or agreeable sensation. If we consider the frequencies of these three notes, we see that they are in ratio of 240cps:300cps:360cps. That is 4:5:6. Therefore by practice, notes having frequencies in the ratio of 4:5:6 give a pleasant or rousing sensation when they are combined or sounded together. Similarly, the triad formed by G, B, and D is also pleasant and rousing to the ear.
If we combine the above triad with a fourth note which is the Octave with 480cps, chord thus formed with 4 notes will still be pleasant. The resultant sound with the combination of notes relative to each other will be in the ratios of 2:1, 3:2, 4:3, 5:4, 6:5, and 8:5, all of them are simple to give a pleasant sensation.
The above common chords which arouse the 'rousing' or the pleasantness or joyful feeling are known as the 'Major' chords.