In music

Music

Music is an art form whose medium is sound and silence. Its common elements are pitch , rhythm , dynamics, and the sonic qualities of timbre and texture...

, a primary triad is a one of the three triads

Triad (music)

In music and music theory, a triad is a three-note chord that can be stacked in thirds. Its members, when actually stacked in thirds, from lowest pitched tone to highest, are called:* the Root...

, or three note chord

Chord (music)

A chord in music is any harmonic set of two–three or more notes that is heard as if sounding simultaneously. These need not actually be played together: arpeggios and broken chords may for many practical and theoretical purposes be understood as chords...

 built from thirds

Third (music)

In music and music theory third may refer to:*major third*minor third*augmented third/perfect fourth*diminished third/major second*Third , chord member a third above the root*Mediant, third degree of the diatonic scale...

, most important in tonal

Tonality

Tonality is a system of music in which specific hierarchical pitch relationships are based on a key "center", or tonic. The term tonalité originated with Alexandre-Étienne Choron and was borrowed by François-Joseph Fétis in 1840...

 and diatonic music, as opposed to an auxiliary triad or secondary triad.

Each triad found in a diatonic key corresponds to a particular diatonic function

Diatonic function

In tonal music theory, a diatonic function is the specific, recognized role of each of the 7 notes and their chords in relation to the diatonic key...

. Functional harmony

Harmony

In music, harmony is the use of simultaneous pitches , or chords. The study of harmony involves chords and their construction and chord progressions and the principles of connection that govern them. Harmony is often said to refer to the "vertical" aspect of music, as distinguished from melodic...

 tends to rely heavily on the primary triads: triads built on the tonic

Tonic (music)

In music, the tonic is the first scale degree of the diatonic scale and the tonal center or final resolution tone. The triad formed on the tonic note, the tonic chord, is thus the most significant chord...

, subdominant

Subdominant

In music, the subdominant is the technical name for the fourth tonal degree of the diatonic scale. It is so called because it is the same distance "below" the tonic as the dominant is above the tonic - in other words, the tonic is the dominant of the subdominant. It is also the note immediately...

, and dominant

Dominant (music)

In music, the dominant is the fifth scale degree of the diatonic scale, called "dominant" because it is next in importance to the tonic,and a dominant chord is any chord built upon that pitch, using the notes of the same diatonic scale...

 degrees. The roots

Root (chord)

In music theory, the root of a chord is the note or pitch upon which a triadic chord is built. For example, the root of the major triad C-E-G is C....

 of these triads begin on the first, fourth, and fifth degrees (respectively) of the diatonic scale, otherwise symbolized: I, IV, and V (again, respectively). Primary triads, "express function

Diatonic function

In tonal music theory, a diatonic function is the specific, recognized role of each of the 7 notes and their chords in relation to the diatonic key...

 clearly and unambiguously." The other triads of the diatonic key include the supertonic

Supertonic

In music or music theory, the supertonic is the second degree or note of a diatonic scale, one step above the tonic. In music theory, the supertonic chord is symbolized by the Roman numeral ii in a major scale, indicating that the chord is a minor chord , or ii in a natural minor scale, indicating...

, mediant

Mediant

In music, the mediant is the third scale degree of the diatonic scale, being the note halfway between the tonic and the dominant. Similarly, the submediant is halfway between the tonic and subdominant...

, sub-mediant, and leading-tone

Leading-tone

In music theory, a leading-note is a note or pitch which resolves or "leads" to a note one semitone higher or lower, being a lower and upper leading-tone, respectively....

, whose roots begin on the second, third, sixth, and seventh degrees (respectively) of the diatonic scale, otherwise symbolized: ii, iii, vi, and vii^o (again, respectively). They function as auxiliary or supportive triads to the primary triads.
In C major these are:

• I C
• V G
• IV F
• vi Am
• iii Em
• ii Dm
• vii Bdim

In minor

Minor scale

A minor scale in Western music theory includes any scale that contains, in its tonic triad, at least three essential scale degrees: 1) the tonic , 2) a minor-third, or an interval of a minor third above the tonic, and 3) a perfect-fifth, or an interval of a perfect fifth above the tonic, altogether...

 the primary triads are minor chord

Minor chord

In music theory, a minor chord is a chord having a root, a minor third, and a perfect fifth.When a chord has these three notes alone, it is called a minor triad....

s, for example Am, Dm, and Em in the key of A minor, though with the use of melodic and harmonic minor the dominant and subdominant may be major.
Auxiliary chords may be considered parallel and contrast chord

Contrast chord

In music, a contrast chord is an auxiliary chord formed from one of the three primary triads and sharing its diatonic function. Leittonwechselklänge , abbreviated Tl in major and tL in minor....

s derived from the primary triads. For example the supertonic, ii, is the subdominant parallel, relative of IV (in C: a d minor chord is the subdominant parallel, the subdominant is an F major chord). Being a parallel chord in a major key it is derived through raising the fifth a major second (C of F-A-C rises to D --> F-A-D, an inversion of D-F-A). Alternatively, secondary triads may be considered ii, iii, and vi. In C major these are:

• ii Dm
• iii Em
• vi Am

In A minor these are:

• ii Bdim
• III C
• VI F