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In music theory, the key identifies the tonic triad, the chord, major or minor, which represents the final point of rest for a piece, or the focal point of a section. Although the key of a piece may be named in the title (e.g. Symphony in C), or inferred from the key signature, the establishment of key is brought about via functional harmony, a sequence of chords leading to one or more cadences. A key may be major or minor; music in the Dorian, Phrygian, and so on are usually considered to be in a mode rather than a key. When a particular key is not being described in the English language, different key naming systems may be used.
Although many musicians confuse key with scale, a scale is an ordered set of notes typically used in a key, while key is the center of gravity, established by particular chord progressions.
The chords used within a key are generally drawn from the major or minor scale associated with the tonic triad, but may also include borrowed chords, altered chords, secondary dominants, and the like. All of these chords, however, are used in conventional patterns which serve to establish the primacy of the tonic triad.
Cadences are particularly important in the establishment of key. Even cadences which do not include the tonic triad, such as half cadences and deceptive cadences, serve to establish key because those chord sequences imply a unique diatonic context.
Short pieces may stay in a single key throughout. A typical pattern for a simple song might be as follows: a 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 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. 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-era music) the key is deliberately left ambiguous at first. Some arrangements of popular songs, however, will shift up a half-step sometime during the song (often in a repeat of the final chorus) and thus will end in a different key.
Instruments in a key
Certain musical instruments are sometimes said to play in a certain key, or have their music written in a certain key. Instruments which do not play in the key of C are known as transposing instruments. The most common kind of clarinet, for example, is said to play in the key of B flat. This means that a scale written in C major in sheet music will actually sound as a B flat major scale when played; that is, notes sound a whole tone lower than written. Likewise, the horn, normally in the key of F, sounds notes a perfect fifth lower than written.
Similarly, some instruments may be said to be built in a certain key. For example, a brass instrument built in B flat will play a fundamental note of B flat, and will be able to play notes in the harmonic series starting on B flat without using valves, fingerholes, slides or otherwise altering the length of the vibrating column of air. An instrument built in a certain key will often, but not always, have its music written in the same key (see trombone for an exception). However, some instruments, such as the diatonic harmonica, are in fact designed to play only one key at a time.
The key determines what the music is played in. It can be in major or minor.
The concept of Keys in composition and the effects thereof
In Western musical composition, the key of a song has important ramifications for its composition:
- As noted earlier, certain instruments are said to be designed for a certain key, as playing in that key can be physically easier or harder. Thus the choice of key can be an important one when composing for an orchestra, as one must take these elements into consideration.
- In the world of the professional clarinettist, for example, it is common to carry two instruments tuned a semitone apart (B-flat and A) to cope with the needs of composers. Even so, it is not unheard of for a piece published in B-flat to include notes a semitone (or more) below the range of the common B-flat clarinet. The piece must then be played on a more exotic instrument, or transposed by hand (or at sight) for the slightly larger 'A' clarinet. As a last resort, it is also not unheard of for a player to roll up a page of the score and insert it into the end of the instrument in order to lengthen it.
- Besides this though, the timbre of almost any instrument is not exactly the same for all notes played on that instrument. For this reason a song that might be in the key of C might sound or "feel" somewhat different (besides being in a different pitch) to an observer if it is transposed to the key of A. This effect is more pronounced on instruments like the piano where certain notes have more strings associated with them or a thicker string. However, it is observed that some musicians overstate this element, and in fact this is a joke in the movie This Is Spinal Tap where the guitarist, in response to a question about a particular piece, says that it is "in D minor which is the saddest of all keys, I find. People weep instantly when they hear it, and I don't know why."
- In addition, since many composers often utilized the piano while composing, the key chosen can possibly have an effect over the composing. This is because the physical fingering is different for each key, which may lend itself to choosing to play and thus eventually write certain notes or chord progressions compared to others, or this may be done on purpose to make the fingering more efficient if the final piece is intended for piano.
- Tutorial on modulation
- A simple, but accurate, explanation of the function of "keys" in music
- Christian Schubart's "Affective Key Characteristics"