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Extended harmonic techniques expand beyond basic triads and dominant sevenths to include upper extensions (ninths, elevenths, thirteenths), chromatic alteration, borrowed chords, and secondary dominants. These techniques add harmonic color and sophistication while maintaining functional clarity. Skillful use of extended harmony characterizes twentieth-century classical and jazz composition.
You already know that chords are built by stacking thirds on a root, and that adding a seventh to a triad creates the foundational seventh chord. Extended harmony continues this logic: add another third above the seventh and you get a ninth chord; add another and you get an eleventh chord; one more and you reach the thirteenth chord. A complete thirteenth chord technically spans all seven scale degrees stacked in thirds. In practice, composers and arrangers select which extensions to include based on the harmonic texture they want—jazz voicings routinely use 9ths and 13ths while omitting the 5th and even the root.
Chromatic alteration takes an extension and raises or lowers it by a half step to increase tension or color. A raised ninth (the ♯9, sometimes called the "Hendrix chord" in rock contexts) and a flattened thirteenth are among the most common alterations. These altered tones don't undermine the chord's function—a dominant seventh with a ♭9 still resolves to tonic—but they add expressive intensity and a distinctly chromatic flavor. When you hear these alterations, you're hearing tension deliberately amplified beyond what diatonic harmony can produce.
Borrowed chords come from a parallel mode: in C major, borrowing a iv chord (F minor) from C minor adds a darkened sound while retaining functional clarity. The iv chord has a pre-dominant function just like the diatonic IV, but the flat third lends a modal, plaintive quality. Secondary dominants—V7 of V, V7 of IV, and so on—apply dominant function to chords other than the tonic, temporarily tonicizing them. These are already familiar from chromatic harmony study; what changes here is integrating them fluently within extended harmonic textures.
The skill extended harmony builds is harmonic imagination: you learn to hear a chord not as a fixed object but as a starting point. Instead of "this is a G dominant seventh," you begin asking "which extensions or alterations would serve the moment?" Jazz musicians call this chord coloring—the underlying function stays the same while the surface shiver of tension changes. Twentieth-century classical composers—Ravel, Debussy, Scriabin—extended this further still, using stacked fourths or whole-tone sonorities that begin to loosen functional relationships entirely. Extended harmonic technique is the doorway between traditional tonality and those post-tonal explorations.
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