Connecting Chords - Root Motion and Common Tones

Which chords to use and when to place them are now covered. What remains is how to join them.

A chord is not a block; it is several voices sounding at once. When the harmony changes, each of those voices has to go somewhere, and there are principles governing where.

The distance the root moves sets up everything

The starting point is how far the root travels. Since a triad is built in thirds from its root, fixing the root motion automatically fixes the number of common tones.

Root motion	Example	Common tones	Character
4th or 5th	C → G, C → F	1	strong forward drive
3rd	C → Am, C → Em	2	smoothest
2nd	C → Dm, F → G	0	fresh, but harder to handle

Check it directly. C (C–E–G) against Am (A–C–E) shares C and E — two. C against Dm (D–F–A) shares none. C against G (G–B–D) shares only G — one.

This table is not for memorizing; writing out the chord tones regenerates it every time.

The principle — hold common tones, move the rest as little as possible

The basic policy fits in two lines.

1. keep common tones in the same voice
2. move every other voice to the nearest available note

Following that keeps the voices from leaping unnecessarily and produces a smooth texture.

In Fig. 1 the tenor’s G does not move at all, because both V and I contain a G. The rest move by the minimum: soprano D→E (a step), alto B→C (a step), bass G→C (a fourth).

Root motion by a third makes it easier still.

Check

Moving from C to Em, how many common tones are there?

twothreenoneone

Check answer

With no common tones, move in contrary motion

The case demanding most care is root motion by a second. With zero common tones, every voice has to move.

And here, moving them all the same direction always causes trouble.

Sliding all four voices in parallel, as in Fig. 3, leaves the relationships between them completely unchanged. That is four singers producing what amounts to one thickened line, and as harmony it has failed. This is the underlying reality of the prohibition on parallel fifths and octaves, which the next unit takes up formally.

The correct approach is to move the bass against the upper voices.

Parallel motion against contrary motion

▶Parallel (failure)▶Contrary (correct)

Check: Both move from IV to V. The first slides all four voices in parallel, and it sounds less like a chord change than like the whole texture shifting sideways. The second moves the bass against the upper three, and the change of harmony genuinely registers. That difference is what voice independence means.

all voices the same direction

Why strong root motion drives forward

Root motion up a perfect 4th (equivalently down a perfect 5th) is called strong root motion. V→I, ii→V, and vi→ii all qualify.

Why does it feel strong? Because there is exactly one common tone. With two shared notes, as in motion by a third, the change sounds continuous, almost like staying put. With none, as in motion by a second, the connection breaks and the music seems to jump to somewhere unrelated.

Strong root motion is the state of being joined by a single thread. Continuous, and yet unmistakably having moved — that is where the sensation comes from.

It also chains. Following the circle of fifths counterclockwise gives vi → ii → V → I, which is the skeleton of the circle progression.

Chaining strong root motion

▶vi – ii – V – I

Check: The roots climb A → D → G → C, a perfect 4th each time. The sense of closing in on a destination step by step persists all the way to the landing on C. This shape is the content of what gets called a circle progression.

roots A–D–G–C, every one up a perfect 4th

Standard voice motion for V–I and V–vi

Finally, the two connections you will write most often.

In V7 → I, two notes have predetermined destinations.

• the leading tone (B) rises to the tonic (C)
• the seventh (F) falls to the third (E)

The tritone B–F resolves by expanding outward. Observe those two and the remaining voices settle themselves.

V → vi, the deceptive cadence, needs special handling.

The leading tone still rises to the tonic, and the bass rises a step from the root of V to the root of vi. Those two are now moving in the same direction, so the remaining voices must descend to compensate.

The consequence is that the third of vi gets doubled. In C major the third of Am is C, so C appears in two voices.

Check

In a V→vi deceptive cadence, which note of vi is doubled?

The rootThe thirdThe fifthNothing is doubled

Check answer

Looking ahead

The approach in this lesson — hold the common tones, move the rest minimally, use contrary motion where needed — is the premise for everything in the next unit.

From here the texture is fixed at four voices, and the rules get tested by actually writing.

▶ Try connections in the part-writing checker Load one of the correct examples, then pick a chord and move a note. The moment you break a principle it flags it, which is an efficient way to feel out where the boundaries are SATB Part-Writing Checker → ▶ Build a chain of strong root motion Arrange the chords so each root rises a perfect 4th and you have written a circle progression Chord Progression Builder →