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Music Theory - Chords
In music a chord is three or more notes sounded together. In theory these can be any notes, but different combinations produce different musical qualities, and so in practice the notes used will usually be based on a set of guidelines governing the formation and use of chords. The study and use of chords is sometimes referred to as harmony.
Harmony is most strongly associated with western music which bases its musical system around the diatonic major scale. Other musical cultures place less emphasis on this scale and rely less heavily on the principles of harmony.
A Triad is a simultaneous combination of three notes and is the simplest form of chord. The second and third notes are a third and a fifth above the first respectively giving a triad two intervals, both of which are a third. The first, third and fifth of a note's harmonic series (as well as the octave) are the most prominent overtones and this is why triads have a strong sound. There are four types of triad. All span a fifth but the interval between the root and the third varies, giving major and minor triads. Sharpening the fifth of a major triad gives an augmented triad and flattening the fifth of a minor triad gives a diminished triad.
Triads may also be inverted or doubled. An inversion is where the root note is not the lowest in the triad. Doubling creates chords with more than three notes where one of the triad's notes is repeated (usually the root) to reinforce the sound. Doubling the third strengthens the tonality of a chord whilst doubling a fifth increases its stability.
Seventh chords developed from triads and are seen as an extension of them. All seventh chords consist of a root, a third, a fifth and a seventh. Many different seventh chords can be created - ten in all:
If you build seventh chords from each triad of each note of a major scale you get the following sequence:
Major Seventh, Minor Seventh, Minor Seventh, Major Seventh, Dominant Seventh , Minor Seventh, Half-diminished Seventh
Ninth, eleventh, and thirteenth chords are called extended chords.
All you need to do is add the needed extension to the seventh chords. For example, if you need a major 13th chord simply add 9-11-13 to the major 7 chord. If you need a Dominant 9 b11 #13 chord, just add 9-b11-#13 to the dominant seventh chord.
Extended chords must contain the root, third, seventh, and extended note. For example in a 13th chord you can leave out the fifth, ninth and eleventh and still have the sonority of a thirteenth chord. Never remove the 3 or 7 notes, for these define whether the chord is major, minor or dominant. Never remove any of the notes that are to be altered, else it will not be the chord that is called for. In eleventh chords the 9 can be removed. In thirteenth chords the 9 or/and 11 can be removed. Never remove the 1, for it will completely change the chord's property.
Minor chords are often written as a small "m" or min, such as m7 or min7; a slash over the m is also common. Dominant chords are often with D or no letter at all, such as D7 or 7. The dominant chord is sometimes called the Major/Minor 7. Major seventh chords are written as M7, sometime the 7 will have a slash through it.
Secundal harmony is based upon chords constructed with stacked seconds. These seconds can be major or minor,diminished is not normally used because it sounds like a unison and the augmented gives the sound of a third. Chords built from seconds do not have traditional names, such as those built with thirds. These chords are often called chord clusters.
Tertian harmony is based upon chords constructed with stacked thirds. These thirds can be diminished, major, or minor. See above for the common spellings of these chords and their common names.
Quartal harmony is based upon chords constructed with stacked fourths. These fourths can be diminished,perfect, or augmented. Chords built from fourths do not have traditional names, such as those built with thirds.
Quintal harmony is based upon chords constructed with stacked fifths. These fifths can be diminished, perfect,or augmented. Chords built from fifths do not have traditional names, such as those built with thirds.