There are all sorts of online piano course that teach you to play the piano by chords, which is a perfectly valid way of learning to play the piano. From what I gather they teach you about various rhythms that you can use but what I have not picked up from their advertising is how do you know which notes to play. I’m not saying that any of these courses skip this bit, I’m saying that the ads I’ve seen don’t mention it.
So to explain as simply as I can, I am going to use the key of C major as an example. What I will explain can be applied to any major or minor key.
The first step is to number the notes of the scale, so C major should be numbered like this:
1 2 3 4 5 6 7 8 or 1
C D E F G A B C
You should note that the first note and the last note are both called C, so even when it is the 8th note in the scale, it is still considered as the first because it is a repeat of the first.
Before proceeding any further, it is important to note that chords have at least 3 notes in them and when the chords are written as letters and numbers, rather than musical notes, the chord type is labeled according to the internal intervals of the chord and not according to the key of the piece of music. So if we were using C major again, the basic chords that can be used are:
C – C, E, G which forms C major chord
D – D, F, A which forms D minor chord
E – E, G, B which forms E minor chord
F – F, A, C which forms F major chord
G – G, B, D which forms G major chord
A – A, C, E which forms A minor chord
B – B, D, F which forms B diminished chord
If you look carefully, C, F and G are all major chords, D, E and A are all minor chords and the chord starting on B is actually a diminished chord.
So in a piece of music in C major, the most important notes are considered C, F and G. The next important ones are D, E and A. B is rather harsh sounding in the context of C major and both the note and the chord are used to move through to either a C note or a C chord.
In the context of C major (and this can be applied to any major or minor scale), the C is the most important note, so you can always add in extra C’s if the C is used in any of the above chords. If you want to play more notes, doubling up on an F or a G (where they occur) is always a good move. To give you a better idea, here is the above table with the best note to be doubled is underlined:
C – C, E, G
D – D, F, A
E – E, G, B
F – F, A, C
G – G, B, D
A – A, C, E
B – B, D, F
Please note that the F chord can either F or C or both doubled up.
It is important to note that without the middle note, the chord is technically not a chord at all and if you have a lot of understanding about chords, you would be aware that it is the middle note that creates the distinction between a major chord and a minor chord.
Especially with modern music, it is up to you how many notes of a chord you play at the one time and it is important to do some experimenting so you can hear what combinations of a chord sounds best, in each circumstance. The above table is merely intended as a starting place rather a definitive way chords should be played.
The chordal approach to playing the piano, is a valid way of playing the piano and understanding what chords are and how they can be used is absolutely essential.