A piano is indispensible for learning music theory. Piano theory implies the use of the instrument, which in turn implies sound, which of course is what music is all about. However, many music students make the grave mistake of learning music theory on paper only.
Hearing the music first in your mind’s ear and then “for real” on the piano (or by singing) is most important when learning music theory. Far too many students end up learning theory only “in theory,” on paper, and they rarely learn how the music actually sounds. For them, learning music theory is like solving math problems, whereas it is applied theory that is really most important, since that is what will so greatly facilitate learning the piano.
Applied piano theory also means the ability to play the proper harmonies (chords), with proper voice leading, as fast as you can think them. It’s one thing to be able to analyze a I-IV-V-I chord progression in a piece of music, but playing it on the piano, in any key, is another, and much more advanced, musicianship skill.
A further point must be mentioned with regard to piano theory. As I’ve stated in other articles (see Piano Key Chart), the keys are not the notes. This is a point of enormous confusion for many piano students, since it was never taught to them from the beginning or they try to use “shortcut” methods such as “learning piano by chords.” Worse, many teachers are only trained in the very rudiments of music theory themselves (and usually poorly at that), and they inadvertently end up creating this confusion in their students!
Always remember that any key on a piano can in theory play any number of notes, called enharmonic. C, B-sharp, D double flat and A triple sharp all correspond to the key we usually (falsely) refer to as “C”!
Along with listening, this is the most essential point in learning piano theory, and, like listening, it is all too often ignored.
An intimately related point is that so much of listening to music involves psychoacoustic and not purely acoustic phenomena. A chord that sounds consonant in one context may sound very dissonant in another. Further, the same keys on a piano will play, say, both a dominant seventh chord and a German augmented sixth chord. (It’s perfectly safe to ignore this technical vocabulary for now; I just wish to give you a revealing example.)
Let’s say we’re in the key of C major. Listen to the following chord progression:
Don’t worry about the technical details for now, but this is a basic I-IV6-V-I progression in C major. Now listen to the following chord progression:
These examples start with the same chords, but pay close attention to the third chord in each example. Don’t worry if you can’t read the notes just yet (though be sure to Learn to Read Music); here’s what’s important: The same keys are played on the piano, but they’re not the same notes. In the first example, the top note of the third chord is an F (highlighted blue in the example), while it’s an E-sharp in the second example. On the piano they sound exactly the same (since they’re played using the same key), yet they seem to sound totally different, depending on the key in which you’re playing! (Beginners should not be confused by the duplicate use of the word “key” in the English language as it relates to music: Piano “keys” are the buttons we press on a piano, while works of tonal music will be in the “key” of C major, G-sharp minor, etc.)
In the first example, the third chord is a dominant seventh. The E-sharp in the second example, however, makes it something totally different, namely a German augmented sixth… even though they sound the same. (Again, don’t worry about chord names for now, as augmented sixth chords are quite advanced music theory material. Also, for purposes of voice leading I slightly changed the “spelling” of the second and third chords, but that doesn’t affect the harmony.) What’s interesting is that the E-sharp is a surprising harmonic twist that leads from the expected C major, all the way to B major, a very remote key!
This is the reason why you must not rely solely on the piano keyboard when learning music theory. Piano theory needs to be informed by reading music; otherwise you’re merely learning which keys to press, not the actual notes. Your goal should be to develop real musicianship, really to understand the notes you play.