Editing Key (music) (section)

==Keys and tonality==
[[File:Ii-V-I turnaround in C.png|right|thumb|Perfect authentic cadence (V-I [here in [[Dominant seventh|V<sup>7</sup>]]-I form] with roots in the bass and tonic in the highest voice of the final chord): [[ii-V-I progression|ii-V<sup>7</sup>-I progression]] in C [[File:Ii-V-I turnaround in C.mid]]]]

The key usually identifies the [[tonality|tonic]] note and/or chord: the note and/or [[Major chord|major]] or [[Minor chord|minor]] [[Triad (music)|triad]] that represents the final point of rest for a piece, or the focal point of a section. Though the key of a piece may be named in the title (e.g., Symphony in C major), or inferred from the [[key signature]], the establishment of key is brought about via [[diatonic function|functional harmony]], a sequence of chords leading to one or more [[cadence (music)|cadences]], and/or melodic motion (such as movement from the leading-tone to the tonic). For example, the key of G includes the following pitches: G, A, B, C, D, E, and F{{music|#}}; and its corresponding tonic chord is G—B—D. Most often at the beginning and end of traditional pieces during the common practice period, the tonic, sometimes with its corresponding tonic chord, begins and ends a piece in a designated key. A key may be major or minor. Music can be described as being in the [[Dorian mode]], or [[Phrygian mode|Phrygian]], etc., and is thus usually thought of as in a specific [[mode (music)|mode]] rather than a key. Languages other than English may use other [[Key signature names and translations|key naming systems]].

People sometimes confuse key with [[scale (music)|scale]]. A ''scale'' is an ordered set of notes typically used in a key, while the ''key'' is the "center of gravity" established by particular [[chord progression]]s.<ref>[[Willi Apel]], ''Harvard Dictionary of Music'' (Cambridge: Harvard University Press, 1969), 450.</ref>

Cadences are particularly important in the establishment of key. Even cadences that do not include the tonic note or triad, such as ''half cadences'' and ''deceptive cadences'', serve to establish key because those chord sequences imply a unique [[diatonic functionality|diatonic context]].

Short pieces may stay in a single key throughout. A typical pattern for a simple [[song]] might be as follows: a [[phrase (music)|phrase]] ends with a cadence on the tonic, a second phrase ends with a half cadence, then a final, longer, phrase ends with an authentic cadence on the tonic.

More elaborate pieces may establish the main key, then [[modulation (music)|modulate]] to another key, or a series of keys, then back to the original key. In the Baroque it was common to repeat an entire phrase of music, called a [[ritornello]], in each key once it was established. In Classical [[sonata form]], the second key was typically marked with a contrasting [[theme (music)|theme]]. Another key may be treated as a temporary tonic, called [[tonicization]].

In [[common practice period]] compositions, and most of the Western popular music of the 20th century, pieces always begin and end in the same key, even if (as in some [[Romantic music|Romantic-era]] music) the key is deliberately left ambiguous at first. Some [[arrangement]]s of popular songs, however, modulate sometime during the song (often in a repeat of the final [[refrain|chorus]]) and thus end in a different key. This is an example of [[modulation (music)|modulation]].

In [[rock music|rock]] and [[popular music]] some pieces change back and forth, or modulate, between two keys. Examples of this include [[Fleetwood Mac]]'s "[[Dreams (Fleetwood Mac song)|Dreams]]" and [[The Rolling Stones]]' "[[Under My Thumb]]". "This phenomenon occurs when a feature that allows multiple interpretations of key (usually a diatonic set as pitch source) is accompanied by other, more precise evidence in support of each possible interpretation (such as the use of one note as the [[root (chord)|root]] of the initiating harmony and persistent use of another note as pitch of melodic resolution and root of the final harmony of each phrase)."<ref name="Stephenson">Ken Stephenson, ''What to Listen for in Rock: A Stylistic Analysis'' (New Haven: Yale University Press, 2002), 48. {{ISBN|978-0-300-09239-4}}.</ref>