Thumb Under (Finger Crossing)

A hand has five fingers, but an octave of a scale has eight notes, and many runs go further. The thumb-under movement solves that. Going up the keyboard with the right hand, the thumb slides under the middle finger (or the ring finger) to take the next note. Coming back down, a finger crosses over the thumb. The left hand does the same in mirror image: thumb under going down, fingers over going up.

C major, one octave

Right hand going up: 1 2 3, thumb under to F, then 1 2 3 4 5. Coming down: 5 4 3 2 1, finger 3 crosses over to E, then 3 2 1.

Left hand going up: 5 4 3 2 1, finger 3 crosses over to A, then 3 2 1. Coming down: 1 2 3, thumb under to G, then 1 2 3 4 5.

▶Right hand0:07▶Left hand0:07

How to make the crossing smooth

1. Start the thumb moving early. As soon as finger 2 plays, let the thumb begin traveling under the hand toward its next key, so it arrives ahead of time.
2. Keep the wrist level and quiet. The hand glides sideways and the elbow follows smoothly. A twist of the wrist or a jerk of the elbow makes the crossing note bump.
3. Practice the crossing pair alone. Play E–F with fingers 3–1, slowly and legato, until the two notes sound as joined as any other pair. Then F–E with 1–3.
4. Add a few notes on each side. D–E–F–G, then the whole scale, each hand separately before hands together.
5. Listen for evenness. The note played by the thumb after a crossing often comes out too loud. Play it gently on purpose until it blends in.

Other keys

Every major and minor scale has its own fingering, but the idea is the same: groups of three and four fingers joined by the thumb. In standard scale fingerings the thumb almost always plays white keys, where it can reach under easily. Thumb-Under: the Full Scale walks through the movement slowly, and Scales in Every Key gives the standard fingering for all 24 major and minor keys.

The same movement appears in arpeggios, where the thumb passes under a wider gap, and in fast passages of almost any piece. It is the step that takes you beyond a five-finger position.