Chords are stacks of notes that sound together at the same time. At the base of all Chords is the Triad (three note chord). Triads are made up of the root, third and fifth tones as derived from the scale in use at the time. Even when we have a Chord with lots of extensions (notes added to the triad), we find there is always a triad at its base that is either Major, Minor or Diminished.
You will work with Chords throughout your musical career, so a thorough knowledge of Chords is vital. On this page, we are simply looking at Chords in their basic root position form. The theory behind constructing Chords will be addressed in the section on Melody & Harmony. The roman numerals indicate how these Chords function within the scale. A one (I) means as the Tonic or root of the key. A two (II) is the Chord from the 2nd scale degree, and the five (V) is the Chord from the 5th degree (also known as the Dominant).
I Major Chords: Starting from the basic Triad, we can add extensions to the Chord.
I Major Chords (Altered): A Chord can be altered by lowering or raising the 5th of the Chord (5th scale degree up from the root) by one Half Step, a Flat 5 (b5) or a Sharp 5 (#5 or +5). While we always want to "spell" our Chords correctly (a b5 should use a flat, a #5 should use a sharp), some Chords like the CMaj7(#5,b5) have to use a flat for the sharp as the "G" would be too confusing with both a flat and a sharp "G".
I Minor Chords: These Minor Chords function as the Tonic (Key Center) when in a Minor Key, same as the I Major Chords (above) when in a Major Key.
I Minor Chords (Altered): I Minor Chords can also be altered by lowering or raising the 5th of the Chord by one Half Step (same as the I Major Chords).
II Minor Chords: These Chords, while still Minor Chords, function as the II Minor Chord (from the second degree of the scale, not the Tonic).
II Minor Chords (Altered): We can also alter these Chords by lowering or raising the 5th of the Chord by one Half Step. Many upper extensions can be added and altered as well.
V Dominant Chords (Dominant 7th): Dominant 7th Chords function as the 5th (5th Scale degree) in the scale. Dominant Chords contain the "Tri-Tone" (6 Half Steps apart) which helps define tonality. The Tri-Tone is the two Half Steps that exist in the Major Scale (the 4th and 7th scale degrees). Dominant Chords allow for lots of extensions and alterations as they can be built using different temporary scales such as the Eight (8) Tone Dominant Scale (discussed further in Melody & Harmony). Note when the Dominant 7th Chord ads the 11th extension the 3rd is not played (we want to avoid the minor 9th Interval between the 3rd and 11th).
Diminished Chords: The Diminished Chord Triad and the "4 Note Diminished Chord" are both equidistant Chords (stacked in Minor 3rds). This lends itself to an ambiguity not shared by other Chords and allows it to function, or imply, a variety of other Chords.
Other Chord Forms: A "sus4" Chord (suspended 4th) is basically a Triad with an altered 3rd raised to the next scale degree. Example: "C" Triad consists of C-E-G, but when altered to a [Csus4] the "E" is augmented up to the next scale degree (F) and is written as C-F-G. Another type of Chord used a lot in Rock music is the "Power Chord" (also known by other names) which basically uses only the root and 5th of the triad. It can be notated as [C5] or [C no3]. Other variations on Chords can be written with an "add" notice. For example, [CMaj(add9)] would be a "C" Major Triad with the 9th (D) added on top. Different that the Maj9 Chord as the Major 7th is deliberately left out.