Instead, Mozart gives us the key of C major (mm. 60-64), drawing upon the second theme from the Secondary Tonal Area. The move to C major is akin to what is known as a “deceptive resolution,” which we will examine shortly. Suffice it to say, that the key of C major is a refreshing surprise at this point. Let’s listen to the beginning of the Development section, mm. 56-63.1From the key of C major, Mozart uses this same Secondary Tonal Area theme to pass swiftly through the key of A minor (mm. 65-66) and reach the key of G minor (m. 67)—which is the parallel minor of the tonic key and has the same dominant chord, the D major triad. Once Mozart has arrived in the key of G minor, he has essentially arrived home, since he wants to conclude the Development section on dominant harmony.We’ll take a closer look at these details. First, though, let’s consider a “deceptive resolution” of a dominant chord. A deceptive resolution of dominant harmony is accomplished by moving the bass note (from V) up by step (to VI), instead of to the tonic pitch (i). So, in a minor key, instead of the normal chord progression of an Authentic Cadence, V – i, we have V – VI.
A deceptive resolution of dominant harmony is frequently referred to as a “deceptive cadence.” But a deceptive resolution is only rarely a cadence. The deceptive resolution of the dominant chord almost always extends the phrase, because we haven’t arrived on the tonic, as expected.Let’s look at a deceptive resolution in the key of G minor, compared with a standard resolution of dominant harmony to tonic. First, the standard V-i resolution; second, the deceptive resolution, V-VI; then both repeated:First Movement: Development DetailsMozart uses a deceptive resolution of dominant harmony to evade the cadence (that is, to avoid resolving the V chord immediately to the i chord in G minor). And the E-flat major triad to which he instead moves provides the perfect setup for an Augmented sixth chord. And this Augmented sixth chord, built on the bass note of E-flat, provides a strong arrival on dominant harmony when it resolves to the D major triad.Here is a harmonic reduction of mm. 64-70. Observe that, in this passage, we begin still in the key of C major, pass quickly through the key of A minor, and arrive in m. 70 on dominant harmony in the key of G minor.1The time spent in the key of G minor, the parallel minor of G major, also points toward another facet of the Classical style: mode mixture. Mode mixture is that marvelous characteristic of the Classical style, when in a major key we hear harmonies borrowed from the parallel minor.The three great composers in the Classical style—Haydn, Mozart, and Beethoven—were mastersof mode mixture. While they make it sound quite natural, it’s as calculated as any aspect of composition. It involves moving between the parallel major and minor scales, for both melody and harmony.