I don't like the way these artsy people explain it. :) Here's the simplest way to understand it, in my opinion, that will also help you in general when it comes to music theory and its applications:
- Take any note, regardless of key or scale. (That you're building a major chord from this note has nothing to do with the key or scale it's being used in.) We'll go with C, which is the root note of our chord.
- Count up 4 half steps to the next note, E, which is the third note of our chord:
- From the third note, E, count up 3 more half steps to the next note, G, which is the fifth note of our chord:
And there you have it:
C E G.
So you can do this from any starting note for any chord type. There are multiple ways of looking at this, pick whichever you like:
- For any major chord, in terms of half steps up from the root note,
0, 4, 7.
- For any major chord, in terms of half steps up from the
prior note, it's
0, 4, 3.
While we're here, minor is a very simple adjustment:
- For any minor chord, in terms of half steps up from the root note,
0, 3, 7.
- For any minor chord, in terms of half steps up from the
prior note, it's
0, 3, 4.
C Eb G.
Thinking this way will help you with a lot of other music theory concepts as well.
For instance, for a diminished chord, you just take a minor chord:
0, 3, 7, and you lower the fifth note:
0, 3, 6. Thus, a
C dim chord would be
C Eb Gb.
For an augmented chord, you just take a major chord:
0, 4, 7, and you raise the fifth note:
0, 4, 8. Thus, a
C aug chord would be
C E G#.
Basically all chords are constructed and modified this way, and this will help you with different scales, because the scales will depict which notes to use in your chord to fit with the key you're working in. If you know anything about music modes, you'll notice that all these are are regular keys (Ionian) which have all of their whole/half steps shifted. That's all. It's all relative!