Could someone accurately describe this method?
Accurate description probably not possible. Best way is to have someone (who knows what they are talking about) to show you. I will give it a try.
1. Place your right hand on the desk in front of you (I am assumning you are at the computer so it would be a drag to go forth and back to the piano), pretending is a keyboard. Keep your fingers parallel to the keys, slightly arched as you would do. Now - without moving anything else, fingers, hands, wrists, forearms, or arms – move your thumb top the right, under your hand. How far can you reach? It will be different for different people. It will depend how long is your thumb (mine is not very long), and how flexible your thumb joint is (I am extremely flexible). I can actually move my thumb so much under my hand (without moving anything else) that its tip appears on the other side. Notice that although you may kike to call this a “lateral” or “sideways” movement of the thumb, it is actually a “vertical” movement of the thumb, completely analogous to the vertical movement of the remaining four fingers. This is important. So let me say a bit more about it. The other four fingers when playing, go “up and down” if we take the nail and finger pad as reference points. Likewise, if you take the nail and fingerpad as reference points, the thumb movement when going under the hand is also “up and down”. It only looks “sideways” because the thumb opposes the other fingers. Anyway, this is the “thumb under” movement in splendid isolation.
2. Now let us try to do the same thing but bringing the thumb over the hand. If you do not move anything but the thumb, it will be nearly impossible. With all my thumb flexibility, I hardly manage to bring it over the second finger. So, as you correctly surmised, you cannot have a “thumb over” movement in isolation.
3. Now let us return to the thumb under movement. This time you are allowed to rotate your arm as you pass the thumb under. You can accomplish that by fixing one of the other four fingers on the desk/keyboard) and pivoting the hand on that finger. Try it with the second finger held firmly in place, then the third finger, then the fourth finger, then the fifth finger. Your elbow will most likely rise, but it is possible to limit the movement to a rotation of the forearm, so that the elbow is barely involved. Pivoting on the third and fourth finger are the most used in orthodox scale and arpeggio playing, but pivoting on the second is also common, with pivoting on the fifth finger being the least used. By adding this extra movements on other parts of the arms, bringing the thumb under becomes far more negotiable (as compared with moving the thumb in isolation). What about doing that with the thumb over?
4. If you roll your whole hand (engaging the arm and forearm to help), it is now possible (although extremely awkward) to bring the thumb over the hand. But why would anyone want to go through this trouble? So we must add another movement to it: we must get the other fingers out of the way. If as you turn your hand you retrieve your fingers (like in making a fist), not only you will be able to pass your thumb over, as you will be playing with the pad of the thumb (as opposed to the side of the thumb). But you may also notice that a lot of arm-forearm and even shoulder movement will be involved to accomplish this strange and still awkward movement.
5. Now let us try another set of movements. The logic behind this next set of movements goes as follows: the best (more efficient) movement for the thumb is “sideways” that is the side of the thumb hits the key – not the finger pad. Likewise, the most efficient movement to the other four fingers is “up and down”, that is the nail is uppermost and the finger pad hits the keys. When bringing the thumb under the hand, or over the hand (as described in item 4) the thumb is immediately in a disadvantage in regards to its most efficient manner of playing. However, if you slant your hand to the right (anywhere from 30 to 60 degrees) in relation to the keys (before you were keeping your fingers parallel to the keys, remember?) then there is no need for the thumb to go under the hand any more. Likewise. If you slant the hand to the left, the thumb can easily go over the hand (it will not really “go over” because the hand is no more there). And best of all, in both cases (under or over) the thumb will be hitting the keys on the side, which is the most efficient way.
6. Finally, keep your hand parallel to the keys again. This time simply move your hand sideways so that the thumb hits the next note in its best position. For instance if you are playing the C major scale, play CDE (fingers parallel to the keys), then reposition your hand on FGAB, and play the F with the thumb.
There are more possibilities than the ones described above, but these are the major ones. So what should we conclude from the above?
a. Thumb under and thumb over are linguistic shortcuts at best and misleading misnomers at worst. The movements involve far more than the thumb, and in particular item 6 is really about elbow and upper arm movements, and not at all about fingers.
b. The movements described are almost never used in the isolation described. Most likely a combination of them will be used (you will be slanting your hands, rotating the forearms, moving laterally and passing the thumb over or under at the same time and at different degrees).
c. Most important, the specific combination of co-ordinations will depend on your physical capabilities (everyone has different hands which cannot be changed – and suppleness capabilities which can be improved to a certain extent), and of the particular musical effect you are trying to convey.
Therefore, practice has to be divided in two stages: Stage 1 is investigation and exploration of the best co-ordinations/movements – given your personal limitations – for the musical expression of the particular passage you are working on. Stage 2 – Ingraining into your subconscious the best you could come up with in stage 1.
Thumb under is essential for slow passages that must be rendered legato. Thumb over is essential for fast passages, where the complications of bringing the thumb under the hand would result in jerky playing. But ultimately, you must have a very clear idea on how a passage must sound, and keep experimenting with different sets of movements until you find the one that conveys it the best.
I hope this helps.
Best wishes,
Bernhard.
P.S. This enormous posting is to celebrate my full member status!
Topic: Thumb Over/Under?