Why do I need a metronome when I am practicing piano?
Perhaps your piano teacher has told you to buy a so-called metronome, or you have heard of this device somewhere and is wondering whether it would be good for you or not.
What the metronome does is counting the time exactly, giving you a particular number of beats per minute. If you haven't got one, but would like to get the general idea, just think of a watch, which will give you a pulse of 60 beats per minute. Now, the watch can only give you seconds, while the metronome will be happy to divide the minute in almost any other number of beats, especially if you have a digital one.
Some composers have used this possibility to tell performers exactly in which tempo they would like their music to be played. You may find the instruction 'quarter note=72' at the top of your sheet music page. You then set your metronome to 72 and count the quarter notes accordingly.
Problems with metronome markings
This is the most basic way of describing the use of the metronome, which however has its complications and pitfalls. For example, it is quite evident that it is hardly possible, and certainly not desirable, to play any piece of music with such a mechanical, unchanging pulse as the metronome gives you. The pulse of music should more often than not be flexible, just like the heartbeat of any living thing. Beethoven, for instance, put metronome marks on some of his works, but at the same time gave the instruction that it only ever applied to the very first measure of the piece.
Also, you should be aware that there are a lot of metronome marks around that are rarely or never followed. This can be due to a number of factors. It might not be put there by the composer, but rather by an editor, which of course makes it less authoritative. But even if it originates from the composer, there may be reasons to ignore or at least adjust it. Sometimes it might have been put there rather carelessly, to please a publisher, or it might even have been done with the help of a faulty metronome (which was in fact rather common when the device was newly invented).
Conclusion
So the conclusion should be that metronome marks can be useful indicators, but they should never be followed slavishly. When you practice piano, it comes to good use when you have difficulty keeping the pulse. But don't practice long sections, trying desperately to follow its every beep or click. Rather use it to check now and then if you are still feeling the pulse correctly.
Look over the different sections of your piece, and try to find not an exact metronome number, but rather an acceptable interval where you and your listeners will still have the experience of a constant pulse. In the example above, where the instruction was to play the quarter-note at 72, you might perhaps end up accepting everything between 66 and 76.
