A Player's Guide to Chords and Harmony by Jim Aikin Page B

progressions are cadences. A cadence is specifically what happens at the end of a phrase.
    If the last chord in the phrase is a V chord, the cadence is called a half cadence. Figure 4-11 shows a simple progression in the key of G in which the first four-bar phrase ends on a half cadence on D (the dominant of G) and the second four-bar phrase on a full cadence. A cadence in which the I is preceded by a IV rather than a V, as in the "Amen" that ends many hymns, is called a plagal cadence.
    If all V chords were followed by I chords, the world would be a dull place. Composers often trick their listeners by leading up to a V chord and then following it with something other than a I chord. This is called a deceptive cadence. The chord most often substituted for the I in a deceptive cadence is the VI (see Figure 4-12). One reason the VI is often chosen is because the VI and the I share two notes (the tonic and mediant), which makes the substitution sound natural. Another reason is because the VI is a minor triad, whose piquant sound adds meaning to the deceptive cadence. Other chords can be used in deceptive cadences, as Figure 4-12 suggests.

    Figure 4-11. This eight-bar progression, used in many country and bluegrass tunes, consists of two four-bar phrases. The first phrase ends on the dominant (D in the key of G), making it a half cadence. The second phrase ends with a V-1 progression. Because the last chord in the phrase is a 1, the phrase ends with a full cadence.

    Figure 4-12. In a deceptive cadence, a I chord is expected, as in (a), but instead a different chord is substituted for the I, most often a minor VI. A deceptive cadence using the minor VI is shown in (b). The deceptive cadence in (c) uses a technique we'll look at more closely in Chapter Five: The E major triad is not part of the key of C major, but instead is a secondary dominant leading to the A minor triad. In other words, although this progression is in C major, it contains a V-I progression in the key of A minor.
     

MAJOR & MINOR KEYS
    Up to now, we've been talking about major scales and mostly using progressions in major keys as examples. Many pieces of music are written, however, in which a minor chord is used as the tonic. Such pieces are said to be in a minor key.
    Each of the 12 key signatures can be used either for a major key or for the minor key that uses (mostly) the same set of accidentals. The minor key in this case is the one whose scale starts on the VI of the major scale. For instance, A minor corresponds to C major (because A is the VI in the key of C major), D minor corresponds to F major, and so on. The key of A minor is said to be the relative minor of the key of C major. In the same way, E minor is the relative minor of G major, F# minor the relative minor of A major, and so on.
    We can use the same terminology when referring to notes and chords in a minor key that we would use in a major. Figure 4-13 shows how the basic terms would be applied to the key of A minor. As you play this example, you should notice one or two important things. First, because the diatonic triads in A minor are exactly the same as those in C major, it's a little difficult to tell, simply by listening, which key you're in. Your ear may tend to drift back toward hearing the music in C major, because the major scale exerts a kind of magnetic pull. Second, the dominant and subdominant triads in the minor key are minor triads. Because of this, the dominant-tonic progression in particular isn't very forceful.

    Figure 4-13. Diatonic triads in the key of A minor. As noted in the text the term "leading tone" is usually used to refer to the note below the tonic, not to an entire triad built on that note.
    The solution to both of these difficulties, which has been commonly used by composers since before the time of Bach, is to alter the 3rd of the dominant when the music is in a minor key. In the key of A minor, more often than not a composer will use an E major chord as the