Tonicization

In music, tonicization is the treatment of a pitch other than the overall tonic (the "home note" of a piece) as a temporary tonic in a composition. In Western music that is tonal, the song or piece is heard by the listener as being in a certain key. A tonic chord has a dominant chord; in the key of C major, the tonic chord is C major and the dominant chord is G major or G dominant seventh. The dominant chord, especially if it is a dominant seventh, is heard by Western composers and listeners familiar with music as resolving (or "leading") to the tonic, due to the use of the leading note in the dominant chord. A tonicized chord is a chord other than the tonic chord to which a dominant or dominant seventh chord progresses. When a dominant chord or dominant seventh chord is used before a chord other than the tonic, this dominant or dominant seventh chord is called a secondary dominant. When a chord is tonicized, this makes this non-tonic chord sound temporarily like a tonic chord.

Using Roman numeral chord analysis, if chord ii comes after V, a harmonic analysis of this sequence of two chords will label the V chord as "V/ii" (colloquially referred to as "five of two"), then ii has been tonicized. So, in a piece in the key of C major, the ii chord is D minor, because D is the second scale degree in a C major scale. The D is minor because to construct a triad over D using only the pitches available in the key of C major—i.e. no sharps, no flats—the triad must be minor—the individual notes D, F and A. The V/ii chord is composed of the pitches in a V chord in the key of ii (key of D minor). The pitches used in a V/ii in this example include the notes A, C# and E (creating an A major chord). In the key of D minor, an A major chord is the dominant chord. In the key of C major, C sharp is an accidental. One can often find examples of tonicization by looking for accidentals, as there are always accidentals involved in tonicization. However, it is important to note that the opposite is not true—just because there is an accidental does not mean that it is definitely a case of tonicization.

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