This lesson introduces seventh chords and borrowed chords.
If you already have experience with seventh chords from the chords ear training section, then these should not be too difficult to identify in a chord progression. To find the diatonic seventh chords in a major key, go back to your chart of diatonic triads and add a seventh on top of each chord (remember to keep the notes within the key). In the functions, a "7" is added after the roman numeral to show the difference between a regular triad and a seventh chord. The possible diatonic functions in a major key are: I7, ii7, iii7, IV7, V7, vi7, and viio7. I and IV are major seventh chords, ii, iii, and vi are minor seventh chords, V is a dominant seventh chord, and vii is a half-diminished seventh chord.
Borrowed chords are chromatic (non-diatonic) chords because they contain notes that are not in the key. If you are in a major key, you can "borrow" chords from the parallel minor key (C major and C minor are parallel keys) to add more variety and interest to your chord progressions. This is also a great way to introduce chromatic tones into a melody or progression without traveling too far outside the key. If a borrowed chord is still based off a diatonic chord tone within the key, then write the function as the roman numeral showing the correct quality of the chord (upper-case for major, lower-case for minor). For instance, if you are in the key of C major, an F minor chord would be a borrowed chord because it is diatonic in C minor but not in C major. Since it is based off the subdominant and is minor, you would write "iv" for the function. If a borrowed chord uses a non-diatonic scale degree, then you must add an accidental before the numeral. For example, a Bb major chord would represent a diatonic VII chord in C minor, but Bb is not diatonic tone in C major, so if you play Bb major in the key of C major, write the function as bVII (the flat accidental shows that you have lowered the actual scale degree by one half-step).
There are many more possibilities for chords in these progressions with these additions, so focus on identifying specific details each time you listen to the progression. What is the bass movement? What quality is each chord (and is it a seventh chord or a triad)? What is the function of each chord? Which chords are borrowed chords and how do they alter the sound of the entire progression?
