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A chord is a harmonic unit with at least three different tones sounding simultaneously. This could be any combination of notes, in any octave and on one or several different instruments. Strictly speaking, a triad is any three-tone chord. However, in western music (1600-present), the term implies three notes built in stacked thirds (one 3rd placed upon another.) The word "root" is the note upon which a chord is based. a C Major triad refers to a Major triad whose root is C. Four types of triads are common in western music. The most widely recognized is the Major triad. It consists of a minor 3rd stacked on top of a minor third (C-E=M3, E-G=m3.) A minor triad consists of a Major third stacked on top of a minor 3rd (D-F=m3, F-A=M3.) A diminished triad consists of two minor thirds stacked on top of one another (E-G=m3, G-Bb=m3.) An augmented triad consists of an augmented third stacked upon a Major third (G-B=M3, B-D#=aug3.)
Each degree of the seven tone diatonic scales has a name to describe its function in the musical sense. Both the Major scale and all the forms of the minor scale share these names:
| Scale Degree | Name | Meaning |
|---|---|---|
| 1st | Tonic | Tonal center, final resolution tone |
| 2nd | Supertonic | One step above Tonic |
| 3rd | Mediant | Midway between the Tonic and the Dominant |
| 4th | Subdominant | lower Dominant, the fifth tone down from Tonic |
| 5th | Dominant | next most important after the Tonic |
| 6th | Submediant | lower Mediant, half way between the Tonic and Subdominant |
| 7th | Leading Tone | has a strong pull towards the Tonic, "leads". |
| 7th | Subtonic | used only for the natural minor scale, the seventh degree is a whole step below the Tonic |
These names are applied both to the scale degrees and to the chords based upon them. The triads built upon the Tonic, Subdominant, and Dominant are often referred to as Primary Triads, because they are the main basis for the tonal system.
Additional notes can be added to triads to form larger and fuller chords, however the more that becomes added, the more dissonant the chord gets. The notes follow the stacked thirds format. The next largest chord after a triad is a 7th chord, which adds a note a 3rd away from the fifth. Whether or not that note is a Major third or a minor third depends on the root. If the root is the tonic in any key except natural minor, then it will be a Major third from the 5th. The thing to keep in mind is that the note must stay in the key. Also, 9th, 11th, and 13th chords are also common in western music, especially in jazz and blues.
When analyzing a piece of music, chords are one of the first things you try to figure out. There is a roman numeral system that corresponds to each type of chord. Upper case roman numerals refer to a major chord (i.e. I, IV, V, etc.), lower case refers to a minor chord (i.e. v, vi, ii, iv, etc.), lower case numerals with a ° denote diminished chords (i.e. ii°, vii°, etc.), and upper case numerals with a + means an augmented chord (i.e. III+, VII+, etc.) It is commonly known that a Major chord is the most stable, and a minor is quite stable, while augmented and diminuted chords are quite weak and are hardly ever used as a resolution point.
