Fun with substitutions
It’s high time to throw out your I-IV-Vs and throw caution to the wind. If you’re not familiar with harmonic analysis, check out this great overview before you read any further.
Still here? Awesome. Lets start by substituting II for ii in a major key. Changing the chord quality from minor to major raises the third a half step, introducing a non-harmonic tone (specifically, a b5) The result? The b5 resolves down to a 4, which means that II is an effective chord to move to the subdominant. Alternately you could move from the II to a ii, a common way to set up a ii-V7. A side note — consider using a II7; the lowered seventh is a good way to add tension.
in C: D - (D F# A) moves to F (F A C) or Dmi (D F A)
Example: “Just an Old Fashioned Love Song”
III in a major key is a good way to move to IV, vi or ii (IV, vi, and ii are related, as they share common tones — vi shares the root and third with the subdominant, and ii shares the third and the fifth). Raising the third half a step introduces the #5 scale degree, which resolves upwards to 6. In some cases, the #5 will resolve downwards; for instance, in III-VI7 the #5 scale degree resolves down half a step to become the lowered seventh in the VI7 chord.
In C: E (E G# B) moves to F (F A C), Ami (A C E) or Dmi (D F A)
Example: “All of Me”
Our last one for today, the omnipresent iv. This is a good substitute for a dominant chord; many songwriters will move from IV to iv before going back to I. The lowered third in the iv chord is the b6 degree, which most commonly resolves down half a step to become, for instance, the fifth of a I chord. However, the b6 can resolve upwards as well; the b6 could become a 6, making it the root of a vi chord.
In C: Fmi (F Ab C) moves to C (C E G) or Am (A C E)
Example: “I Believe I Can Fly”