But you said after 7 repetitions, you won't learn the passage any better. Now I'm confused completely. o_O
Ok. I will try again.

Let us say that you decide to practise the piano 5 hours everyday. You have several options on how to go about allocating this time. You could for instance, sit at the piano and stay there practising for five hours solid. This is not a good idea. A much better way is to divide this five hour period into practice sessions lasting 20 minutes plus 5 minutes rest. If you do that, you will have 12 practice sessions (25 mins x 12 = 5 hours). Are you with me so far?
[if you decide to practise the piano for one hour everyday, you can still follow the same scheme, but this time you will have only 3 practise sessions, instead of twelve. Or you can practise ten hours a day, in which case you will have 24 practice sessions.]
Now what should you practise in each of these 20 minutes practice sessions? I will use as an example the Prelude in F#m (WTC1), since this is one of your pieces. Let us say that your aim is to master this prelude (I will not deal with the fugue, just the prelude). How should you go about it? Let us also see
how you should not go about it.
1. I will assume that before getting even near to the piano, you will have:
i. Listened to a CD of this piece with the score in front of you. In fact I would suggest that you listen to several different pianists (and some harpsichordists as well) interpretations of it.
ii. Made a motif analysis of the prelude.
iii. Made a harmonic reduction.
iv. Made a copy of the score where the three voices (bars 1- 2, 12 – 16, 18 – 19 and 22 – 24) have been isolated, the fingering written out and the distribution between hands been sorted out (in this prelude this is straightforward: the RH plays the treble clef, the LH plays the bass clef).
v. Sight read through it to identify the most difficult (for you) bars/passages.
[why not ignore all this and simply jump straight away into playing it? Very simple: It is almost impossible to memorise something that is meaningless. Meaning is what allows associations and memory is based on associations. The analysis above will show you the
meaning of this prelude. After you finished this preparatory work, give a lecture to willing friends/family on this prelude. This will guarantee that you never forget what you found out about it in your analysis].
2. Having done the above work (mostly) away from the piano, you are ready to spend 5 hours a day working on mastering this prelude.
[One way, is of course to plunge into it for five hours solid. Start on bar 1 and read through to bar 24. Then start again and repeat as many times as you can fit in 5 hours. Do not get away from the piano during these five hours. Needless to say this is the worse thing you can do. First you will not learn the prelude this way in one hundred years. Second you will get so many bad habits that you will probably be unable to master it even if you change your way of practising later on. Thirdly you get burn out. Fourthly you most likely get injured].
So, as I said divide your five hour into 12 sessions of 20 minutes with a five minute break in between (if you are going to do all 12 sessions consecutively – but you can also do 4 sessions in the morning, 4 in the afternoon and 4 at night, or any other distribution that fits your schedule).
Now what you are going to do in your first 20 minute practice session? You are going to work on a section of the prelude. Which section? And how large should this section be? Only one bar? Two or three bars? 12 bars?
This will depend ultimately on you. How much technique you have under your belt, how much facility you have with playing counterpoint, how much of the technique needed to play this piece you must acquire.
The important principle is this: whatever section you choose,
it must be completely mastered and memorised at the end of the 20 minute practice session.. This means that if you decide to work on bars 1 – 4, at the end of 20 minutes, these 4 bars must be
perfect.
It takes about 1 min. 30 sec. to play this prelude. So if you are to play the whole prelude, which means that you will probably be able to fit about 10 repeats of it in 20 minutes. Obviously 10 repetitions will barely be enough to master this prelude. So the full 24 bars is obviously too large. On the other hand it may be a waste of time to spend 20 minutes on the first bar.
That’s where the seven repetition principle comes in. Choose a chunk of the prelude
with separate hands, say the first four bars. Can you master each hand separately after seven repeats? Can you play each hand perfectly with the correct fingering, the correct rhythm, and memorise it after seven repetitions? Let us suppose you cannot. After seven repeats the whole section is still falling apart. Your fingers keep going to the wrong notes, or you keep using the wrong fingering with the consequence that your fingers are tying themselves in knots and you have to compensate by using all the wrong movements. Moreover you keep forgetting how the passage goes, so that you are still having to read it. If this is happening, do not keep repeating after the seventh time. It will be not only a waste of time, as you will be learning all the mistakes you are making.
You have chosen a far too large passage to master, and insisting on repeating it will not make any difference. So
cut it in half. You must be ruthless here. So now you are going to try two bars only. Another seven times, and the same thing happens again. So cut it in half again.
Now you repeat just the first bar (hands separate still) and this time after the fifth repeat you experience that magical moment when your fingers start to do everything right and you have actually memorised the whole bar. Excellent. You have found the passage you are going to be working on. Chances are that by now your first twenty minute session is over. So stop, get out of the piano, go out, stretch, drink a glass of water, watch the latest news, in short anything to take your mind of what you have just done. Take a five minute break!
3. Now go back for another 20 minutes. This time you know exactly what you have to do: master completely that first bar. As you sit at the piano, you may experience a very common occurrence, so get used to it, it is no big deal.
It will feel as you have never seen the passage you just practised before. Most students who are not told to expect this to happen get really discouraged at this point. But as I said it is no big deal. Just go back to hands separate and work on it again. It will come back very, very quickly.
It is now when everything is perfect that you can actually start to practise. So you see, the 7 times repetition you did do not really count as practice. It is just a practical way to figure out the size of the passage you will be working on. This is also the reason why you must always do it with separate hands. If you go for it hands together, all the mistakes you are making while investigating the best way to play the passage will get ingrained in your hand memory form where it will be almost impossible to dislodge them. If you do it with hands separate nothing gets into your hand memory, so hands separate is a very safe way to try different things that you may discard later as inappropriate.
So spend the next five minutes or so playing that first bar with hands separate. Since this is pretty unchallenging you will be able to fit in hundreds of repetitions. You can play in rhythm variations, in chords (particularly useful on the RH), you can play utlrafast, ultra slowly.
Now spend the remaining of the practice session working on hands together. Since hands together are 37 times more difficult then hands separate, even though you completely mastered HS, it will take much more time to master and memorise HT than it took HS. Also you want to be extra careful with not making any mistake whatsoever at this stage, since it when you play HT that hand memory is formed. In any case, by the end of the practise session this first bar should be completely mastered, memorised and pretty much ready for performance.
4. At this point comes the 20 minute principle.
Do not play this first bar anymore today! Nothing bad will happen if in your next 20 minute practice session you work on this first bar again. But nothing good will happen either: It will be a total waste of time. Instead take your break, and on the next session
work on a different passage of the prelude.
5. It is very important that you understand that although you apparently mastered the first bar on your 20 minute practice session, this is far from the truth. Learning is done by the unconscious mind. So you need a night’s sleep to integrate whatever you learned today. This means that your mastery of the first bar is temporary and it will remain so until it is incorporated by your unconscious mind. One consequence of this, is that the next day, when you play through the first bar you had completely mastered the day before it will be as if you have never seen it before. Learn to expect this. Accept it. Although it will feel at the moment that you will have to start form scratch again and go through all the drudgery of the previous day, this is far form the truth. Typically, it may have taken you 20 minutes to master the first bar on the first day. On the second day – even if it feels just like when you first set eyes on the passage – you will master it again at a fraction of the time it took you the first day. Maybe five minutes. So master it again.And again do not touch it until the next day.
6. Come the next day, the whole story repeats itself. But again you will remaster the first bar in a fraction of the time, maybe one minute this time. And then by the forth day, you will go to the piano and play it perfectly first time. When this happens the passage is yours forever. You will never forget again (pretty much like you will never forget your mother tongue, or how to ride a bicycle). However for this to happen you must go through exactly the same steps every day you did o n the very first day. Most people cut corners and that is why they are forever struggling with the same piece.
7. Now, do not forget that you are not working only on the first bar. You have another 11 sessions during the day. If in each you were working on a different bar, this means that over the first day you worked on 12 bars of this prelude. On the second day, because it is taking much less than 20 minutes to relearn the 12 bars you have learnt on the first day, you will probably be able to start another six bars. On the third day, you will be able to easily fit the remaining six bars and start using the practice sessions to join bars, so now on your practise session you may be working on passages that are 2 or 3 bars long. I estimate that it should take 4 – 5 days to completely master and memorise this prelude for someone with no technique (the technique being acquired as one works on each section – for the Hanon lovers amongst you, check out bar 20: repeat it 30 times and you have a Hanon exercise right there, staring you in the face). This of course is subjective some people will take more time, some people less time. But the point is, which approach will deliver the goods in less time? There is only one way to know. Select another prelude of similar difficulty. Learn one using the approach I am suggesting. Learn the other using whatever is your favourite way. See which method is best. Then tell us the results. If your method is better, describe it in detail, so we can use it as well.
8. To sum it all up: There is no point is spending more then 20 minutes (make it 30 if want – but I have got away with as little as 10 minutes practice sessions) in any passage. As soon as you master it, drop it until next day. If you cannot master a passage in 20 minutes, it means that the passage you chose to work on is too large. Cut it in half. Now it would be silly to spend 20 minutes practising something only to discover at the end of 20 minutes that it was too large. So investigate the size of the passage by repeating it 7 times. If you can learn it (which is very different from mastering it) with 7 repeats, I guarantee that you will be able to master it in 20 minutes. Always do your investigation with hands separate in order not to ingrain mistakes and inappropriate movements/fingerings in your hand memory.
Best wishes,
Bernhard.