Stacking Thirds Lying Down
Understanding chords as groups of intervals has its advantages. One of those advantages is that it makes spelling chords easier. Instead of memorizing the notes that make up every chord, you can use the intervals to identify the notes.
For instance, if you know that a diminished 7th chord is made up of three minor 3rd intervals, you could overlay that on top of any Chromatic scale to arrive at the notes of this chord in every key. Below are seven Chromatic Scales and below them are some common chords showing the intervals that make them up stacked horizontally.
For the sake of illustration, displaying the chord intervals in a horizontal position is helpful. However, you will often hear people talk about staking thirds. This is another way to think of chord construction and one that is helpful for reading music. In fact, the distance between the lines on a musical staff are a third apart. Likewise, the distance between the spaces on a staff are also a third apart.
As an example, a Cmaj7 chord is made up of the notes C, E, G, B. Either horizontally or vertically stacked, the intervals of this chord are: maj 3rd, min 3rd, maj 3rd. These intervals in this specific order always produce a major 7th chord no matter what the beginning note is.