Doc Snow has been an online writer for over seven years. He's a lifelong musician who loves to record his own compositions.
This article investigates the patterns governing triads in second inversion. Here, you will learn to navigate the tricks and traps with video examples and interactive practice questions! Let's get to it!
It probably sounds as though second-inversion triads--also known as 'six-four chords'--are a bit different from root position and first-inverrsion triads. If so, then the impression given is entirely correct. Traditionally, chords were classified by the intervals they contained, reckoning things upward from the bass tone.
According to this view, root position triads were the most stable, since above their bass tones one would find a perfect fifth and either a minor or a major third. (Diminished and augmented triads are considered dissonant in this position, precisely because their chordal fifths are not the stable perfect fifth, but the decidedly unstable diminished or augmented fifth.)
Less stable are first-inversion triads; they contain a minor or major third, just like the root position triads, but substitute a sixth for the fifth. Both intervals are consonances, though the sixth is less stable than the fifth. Still, first-inversion triads may be used quite freely, as we have seen.
By contrast, second-inversion triads are characterized by an unstable fourth, as well as the more stable sixth. That fourth above a bass tone had, by the time when chordal theory was coalescing, been treated as a dissonance for many centuries. Therefore, the second inversion triad took on a somewhat dissonant quality too.
That does not mean it is not a useful sonority, however. It just needs a little care to use appropriately. We'll examine in turn the normal ways in which sixth-four chords appear in common-practice music.
Alternating and Arpeggio Six-Four Chords
These two patterns are closely related, and operate on the same psychological principle. In both cases, the root position voicing of the triad occurs first--and very often on a strong beat--and is then and only then followed by the second-inversion voicing. This sequence allows the instability of the six-four to be subsumed in a larger, and stable, context. So the second-inversion triad can freely follow the root position voicing of the same chord--even, in a pinch, the first-inversion voicing. But the reverse does not work.
So what differentiates the alternating and arpeggio six-four chords? In a word, the melodic pattern of the bass. Here is how the alternating six-four works, as shown in a lead sheet for the American folk song, "John Henry."
Note how the bass works in the first measure. Although the entire measure falls within a G major chord--see the chord symbol above the treble staff?--the bass alternates between root (beats one and three) and fifth (beats two and four) of the triad. That is the origin of the term 'alternating.' Note, too, how prevalent this pattern is throughout the excerpt--it is not uncommon for this style of bass to continue for long stretches of music.
By contrast, here is an example of the arpeggio six-four--the setting of "Auld Lang Syne" which we have examined twice before:
Note the many bass arpeggio patterns. (For instance, mm. 1, 3, 5, 9, and 11 all contain arpeggio six-fours.) In each, the arpeggio pattern begins on the chordal root, or sometimes with the third (first inversion)--never with the fifth (second inversion.) It then proceeds through the other chordal members in some variant of a arpeggio pattern. The second-inversion voicing can occur anywhere within the pattern except the beginning; it must be 'prepared' by a root-position or first-inversion voicing.
Again, this is a common accompanimental style, and can continue for considerable stretches.
Let's work an example. If you are new to this series, our standard practice has been to write out questions on paper before looking at the answers given--physically writing out the questions will help you retain the knowledge gained and to build your skill.
Also, while the format of these Hubs lends itself to the voice-by-voice presentation of the answers--and that's how I present them--in reality most composers work on all voices simutaneously, or at least in a rapid-fire back-and-forth process. Working on paper lets you work that way, too.
If you don't have music paper handy, fear not--the sidebar has a link to a site from which you can download and print paper, free.
So let's get to that practice question. First, identify its key (below.)
The key is Bb.
Look at the brackets above the staff; they show where you should write alternating and arpeggio six-four chords. (Hint: One implication of the brackets is that you need to change the chord on beat four of bar two.)
Now write a bass line, using the six-four chords as just explained, starting on second-line "Bb."
Just to get you started, the first two beats should be an alternating six-four chord. The tonic chord is the obvious possibility, since the soprano tone would then be the third.
For any readers who may be unfamiliar with standard Roman numeral chord notation, the Roman numerals given with the bass voice indicate chords (as identified by their roots), with the quality of the chord--major (or minor)--being shown by upper (or lower) case of the numeral.
The vi triad on beat four of bar two is indicated because it differentiates the preceding and following chords: the brackets and their enclosed notes imply that the preceding chord is I, while the succeeding chord is IV. The only other triad containing the soprano's "Bb" is vi.
If your bass line is close to the one shown, differing only in an octave placement or two, don't fret--there are several places where the bass could be an octave higher or lower without creating a part-writing error. If you put a six-four before a root position, or had a chord change in the wrong place, fix those errors. Then go ahead and add alto and tenor.
Let's try one in minor, too. (Not to mention the triple meter!)
Note that this time, the melody includes some passing tones. Ignore them when figuring out the harmonic progression!
Once again, brackets denote the spans--these are often called 'prolongations,' since they extend the harmonic 'influence' of a single chord over a longer time--defined by the arpeggio and alternating six-fours.
Write your bass line.
As you may have noticed, there are two choices for the prolongation beginning bar two--iv and VI.
Both are quite workable, so we'll write the inner parts for both versions, beginning with the submediant version.
Now work out the subdominant version, too. (I'll give the video for the two versions together, just a bit later.)
Which do you prefer?
Neighbor Six-four Chords
In the strict sense of the word, the previous patterns have been linear--that is, they are defined by melodic motion, not by harmonic function. But because of the leaps, some might tend not to think of them by that description; many of us associate "linear" primarily with stepwise motion. But we speak of 'disjunct lines,' too, to describe lines moving by leap.
Those who feel that way may be a bit more comfortable with the 'linear' tag as applied to neighbor six-four chords; they are both linear and conjunct (stepwise.) In the previous Hub we mentioned that 'auxiliary tones' are also called 'neighbor tones.' This term is very much connected with the notion of neighbor six-four chords. Consider this example:
The bass does not change at all, while two of the upper voices execute simultaneous upper neighbor motions. (The upper voice pair may be any of the three possible pairs, though pairing of the upper two is perhaps most common.)
In principle, the neighbor six-four chord could be used to prolong any major or minor triad; but in practice, the chord almost always prolongs either I or V. These are, after all, the main structual chords in common practice style.
So, when looking for opportunities to use a neighbor six-four, one should look for four specific lines--if a neighbor six-four prolongs the tonic, the lines generated will be 5-6-5 and 3-4-3; if the dominant, 7-1-7 and 2-3-2.
Look for such lines in the following melody, then use what you find to write a suitable bass line. There are opportunities (not, I trust, too hard to find) to use two neighbor six-four chords. For good measure, also use a viio6 on beat 2, as indicated by the asterisk.
In this version, the bass sustains through the neighbor six-fours, but this is not necessary. (It is common.) The bass could have repeated the tone instead (either at pitch or displaced by octave), as shown in this variant:
Now write the inner parts--an open voicing will work well to start.
Another question on neighbor six-fours is warranted, but let's be tricky and mix prolongations (with arpeggio or alternating six-fours) in as well.
We'll try the following melody; as in the first question, brackets indicate prolongations using the alternating or arpeggiating six-four patterns. Locations for six-fours are given.
Work out the implied harmonic progression and write the bass.