Our brains naturally navigate towards what we assume is the easiest way to accomplish any given task. But what if I told you that what might seem easiest right now might actually crippling your musical efforts in the long term? And that you might actually be damaging your efforts to learn music?
If you struggle to learn music, if you can't hear music you've never played or heard in your "mind's ear," if you can't recognize essential harmonies, then you're missing the most crucial aspect of learning music: ear training. This is the key to learning to play piano by ear.
Ear training is literally the "listening comprehension" of music. It is without a doubt the single most neglected aspect of music training today. Many teachers fail to systematically train the ear at all, assuming that training the eyes to learn to read music and the fingers to play are sufficient.
Yet since music is sound, ear training ought to be the first and foremost task of any developing musician. This ought to be self-evident. Just as the painter must develop the most acute visual perception and the gourmet chef a refined taste, so must the musician develop acute aural sensitivity.
Our first essential task as students of music is to "open" our ears. This implies learning how listen to music we hear as well as listening to ourselves as we play. This latter aspect of ear training is unquestionably one of the most difficult tasks for the developing musician. It can take many years to synthesize one's inner conceptions with the sounds we're actually producing. In other words, until we're very advanced musicians, the sounds we think we're making simply aren't the ones other people are hearing. (This aspect of playing music obviously has very much to do with technique, which must at all times be married to the ear.) Simply recording ourselves and playing it back will reveal how disparate what we think we're playing and what we're actually playing can be.
The second aspect of ear training is recognizing what we are hearing, just as we recognize objects we see. It is not necessary for a listener to recognize with scientific precision everything he or she hears. It is, however, necessary for us musicians to thoroughly understand the compositional material of every piece we play, just as actors must understand language. Meaning lies behind and between the notes, and it's our job to communicate that meaning. It's impossible to communicate musical meaning if we don't understand the basic vocabulary.
Playing music without this essential ear training would be like trying to speak a foreign language without understanding the words. You could learn by rote—it's indeed possible to learn how to press the right keys in the right sequence simply by repetition, but if you don't understand the actual "words"—the notes, intervals and harmonies, you're merely exercising your fingers. Your fingers are learning, but not your ears. This "muscle memory," as it's popularly called, is infamously unreliable. It's guaranteed to give you serious performance anxiety, and it's a practical 100 percent guarantee (no money back!) that you'll blank out right when you most depend on it.
Tragically, most pianists play like this. They learn entire fugues this way and then have panic attacks when they attempt them in front of others, and memory slips abound. If you're in the habit of practicing like this, the time to break this habit is immediately. Every time you practice with a disengaged ear you will be reinforcing the very habit you're trying to break. Hence, you will actually be doing harm to your musicianship. The more you work improperly, the harder it will be to create retroactively that ever-critical ear-finger connection.
Your goal is to learn to "hear" with your eyes and "see" with your ears. Your fingers must be guided at all times by your inner ear. We shouldn't hear because we play, rather we play because we hear. In other words, we don't hear a note simply because we happen to have struck the right key, we strike the right key because we hear the right note in our mind's ear. This is the essence of getting the mind ahead of the fingers, and this is the ultimate goal of ear training.
The first aspect of this goal is technical: Your inner sound concept must always direct your fingers; that is the aim of technique.
The second aspect deals with pitch and harmony. Your understanding of harmony must be so ingrained that your ear seemingly automatically tells your fingers which notes to play.
If your ear isn't guiding your fingers in this manner, you're on very dangerous territory indeed. Your musical work isn't based on real musicianship; rather, you're "simulating" playing the piano. Recall the language example: It's possible to learn to type the right letters of words and sentences in succession, but in the long run it's infinitely superior, not to mention vastly more enjoyable, to actually know the language. Then you can say anything with ease.
This is the problem with so many "quick and easy" piano methods nowadays, and this is why they fail to create authentic musicians in the long run. They cater to the instant gratification mentality, lazy students fall prey to them, show modest progress at the beginning and later invariably give up in frustration.
Even advanced music students face this problem, since ear training is no longer an integral part of all aspects of music education, but is rather relegated to only a few semesters in a separate course that has no relation to music students' "core" instrumental work. This reveals a gaping hole in their musical education. And it's not the students' fault, it's that of the music educational system. In most cases ear training is never even mentioned until the student enters a conservatory or university program, and then most of class time must be spent on remedial work that should have begun with the very first lesson. How embarrassing that the final exam so often consists of the identical material to the entry exam, only played faster!
The good news is that there's a solution to this problem, and a very large part of that solution is proper ear training. The bad news is that it takes considerable mental effort, and lazy minds would prefer to just exercise their fingers and hope for the best. The effects of this "malpractice" rear their heads at all the wrong times: when it really counts. The deficiencies can be embarrassing. I've encountered graduates of well-known conservatories who could, after much diligent practice, perform extremely difficult pieces but who could not distinguish a major third from a minor third by ear. They learned to learn primarily with their fingers rather than their ears.
What's wonderful about training the ear properly in this manner is that the work is largely cumulative. In the beginning it will require great effort, like running a mile for the first time. Like athletic training, with regular practice you'll develop quickly and will come to enjoy each further step. Yet, also like athletic training, it requires regular practice. The body operates according to a strict "use it or lose it" principle. Ear training therefore needs to be a part of your daily practice regimen.
A simple test to see whether you're learning primarily with your ears or merely with your fingers is to transpose your music (without the aid of the score, of course). Obviously, extremely technically difficult pieces such as etudes don't lend themselves to this sort of ear training, but slower pieces do. Fortunately for us, it's the slower pieces that tend to give us memory trouble since we're unable to play them on "autopilot"; that is, our muscles don't readily take over.
It's also best to use practice pieces rather than performance pieces for transposing, at least at the beginning. Béla Bartók's Mikrokosmos is absolutely ideal for this work, especially since it's so full of surprises. When working with this material it's essential to stay very alert for unexpected notes—you can't simply play notes within a conventional scale or chord.
Another simple but powerful method of ear training is to sing each voice in all pieces you play. This is an especially useful method of testing whether you're really hearing everything. In most cases, students hear only the melody and bass. They tend to have only a vague impression of the vital middle voices and hence the piece as a whole. This accounts for much of their high degree of uncertainty, difficulty memorizing and performance anxiety. Sing each and every note without the aid of the piano, making sure you're staying absolutely on pitch. The piano is used only to give a starting note and to periodically check your pitch. While tedious at first, this method of basic ear training will ensure that you're truly hearing everything and will give you far greater security so that you can concentrate not on playing the right notes but on expressing the music.
If you're using music such as Mikrokosmos, which I highly recommend, be absolutely certain you don't "cheat" and merely sight-read new pieces at the piano! All the ear training value, hidden in the many unexpected melodic turns, is lost forever the moment you press the keys to hear the correct pitch. You only have one chance to do it per piece! Remember, this is exactly the habit we're seeking to correct—the goal is to create an accurate inner musical impression rather than rely on external auditory feedback.
This, by the way, is why Beethoven (and Gabriel Fauré, as is less known) could go on composing music in the face of deafness. Thanks to their impeccable ear training and musicianship, they indeed heard every note.