Playing intervals and chords in the C Major Scale
In this lesson, we will continue to limit the discussion to the C Major Chord scale of all naturals, the white keys. Nevertheless, in playing intervals that start and end just on the white keys, you still have to count the black keys in between them. Below you see the scale presented as a keyboard where the 2nd line is the interval count from the previous note on the scale. Five out of 7 times, there is black key in between so the interval count is 2. The other two times, at the gaps, there is no black key in between so the count is 1.
By the way, this interval sequence of 221 2221 is the definition of a Major scale. All of the 11 other Major scales can be formed by using this same interval sequence and starting on the other 11 notes in the 12 note scale. The C Major scale is the only Major scale comprised of all naturals. All of the others will include from 1 to 5 sharps or flats on the black keys. (FYI the sequence for a minor scale is 212 2122, but this is for another day.)
The goal of this lesson is to try to help you visualize the intervals and chords you'll need to play with one hand in the C Major scale.
visualization of 2-note chords
intervals of 2
The C Major scale has 5 instances of a 2 note chord and none of them cross a gap. Why is that? If you look at the figure above showing the scale on a key board, you can see that each of the 5 instances have a black key between the two notes. But at the gaps, there is no black key (that's the definition of a gap). So the interval between the adjacent white keys is 1. Therefore, the general rule is that when crossing a gap, the interval count must be an odd number. (That is, unless the interval is big enough to cross both gaps, at least a count of 6). And the corollary, when not crossing the gap, the interval count is even
Study the staff at left and visualize the associated keys of each of these five chords on the keyboard. Now go to the keyboard and play them. The nice thing about the C Major scale is that for each of these chords, the notes are adjacent on the white key row (that is, the ones with the black key in between). The exceptions being B-C and E-F (no black key in between). In general, you play the two adjacent white keys with two adjacent fingers.
The visual image to remember is how these chords of interval 2 look with their 50% overlap.
intervals of 3 and 4
The discussion of these two interval counts are combined because in the C Major scale, the 2 note chords look the same! They all look like two cannon balls stacked up.
However, they are not the same, and it's again due to the gaps. Four of the chords have an interval count of 3 and three have a count of 4 (traditionally named a "minor 3rd" and a "major 3rd"). These follow the "rule" described in the previous section with respect to crossing and not crossing a gap respectively. Remember that the gaps are visualized as just below the red and blue lines, in between B and C, and E and F. Thus, on the line is above the gap while touching the line from below is below the gap. So study the staff and decide which ones cross a gap.
Now go to the piano and practice playing these. Even with different interval counts, they're all played the same way: 2 white keys on either side of a white key. Likewise they're generally played with 3 fingers separated by a finger. Thumbs count as fingers here.
The visual image to remember is that you play cannonballs with fingers separated by a finger in order to skip a white key in between. Also remember to "mind the gaps".
intervals of 5
All of these intervals cross a gap. This is because this wider interval is more likely to cross one or the other gaps. So now the cannonballs, AKA noteheads, have a little space in between them (half of a notehead to be exact). Study these and then play them with 2 fingers in between the 2 playing the chord. This of course corresponds to skipping 2 white keys between them.
This interval is known as the "perfect 4th" interval which shows that it is regarded as having a pleasing sound.
intervals of 6
There are only 2 of these in the C Major scale, F to B, and B to F. This interval is infamously known for its dissonance, or unpleasant sound. But try them yourself and you decide. In any case, for most of the tunes you will encounter as a beginner, you're probably not going to see it. So end of discussion of it for now. Let's move on to one more important interval.
intervals of 7
In total contrast to the previous interval, this is the famous "perfect 5th". In music theory it has a recurring importance. There are 6 of them in the C Major scale since it is so wide it's bound to cross a gap. There would be 7 but the B to F interval crosses both gaps and thus has an interval count of 6.
Playing these has you skipping 3 white keys and 3 fingers. Notice, and remember, the even wider space between the noteheads, equal to an entire notehead.
Here is a cheat sheet of sorts showing the 4 principal chords you need to know with intervals of 3, 4, 5, and 7. These examples are centered around the note C but even when moved to another note, the relationships between the noteheads in the chords will be the same. Of course, the trickiest ones are the intervals of 3 and 4 that look alike but differ when crossing or not crossing a gap. And, it turns out the interval of 4 (an even number) is the only one that doesn't cross a gap among this set.
On the keyboard the corresponding C Major white key relationships are:
interval of 3 - adjacent white keys (skip 1 black key)
interval of 4 - white keys separated by 1 white key (skip 2 black keys)
interval of 5 - white keys separated by 2 white keys (skip 2 black keys)
interval of 7 - white keys separated by 3 white keys (skip 3 black keys)
While it is possible to learn every chord by memorization, you will not develop a good sense of generalization whereby knowing the rules you can recognize and play chords with ease. This will be especially valuable when you expand beyond the C Major scale and there are whole new sets of chords to learn.
playing triads (3-note chords)
With that said, there's more. If you are indeed playing only on the white keys, you will not be able to play all chords. For example, you can play C Major, C-E-G, but not D Major, D-F#-A, because F# is a black key. therefore, with the C Major scale, you are limited to the three note chords (or triads) C Major, F Major (F-A-C), and G Major (G-B-D). It turns out there are three Major chords in each of the 24 possible scales, but not the same set of chords (different roots). And FYI, the same is true for minor chords (3 per scale).
This occurs because the two notes span a gap in the black keys. While it's pretty easy to see this while staring at the keyboard, it's a different story when you are trying not to look at the keyboard and are focusing on the sheet music. WYSIWYP notation helps alleviate this by having the red and blue lines at the gaps. Think of the red line as sitting on top of the "crack" between the B and C keys (where there's no black key). A chord with its root below C and it's 2nd note on C or above is crossing the gap. A chord with a root of C does not cross this gap. The blue line works in the same way for the E - F gap.
So with these chords (image of two note chords), practice playing them without looking at the keyboard and being conscious of the gaps. That is to say, "Mind the gaps".