In the last chapter we saw in detail how the three main open shapes are related to each other and how moving the notes in the same 'place' of the shape gives the same resulting chord type. This is obviously not a coincidence since all the three shapes share the same intervals in the same order.
But we could go one step further and say that they're actually exactly the same shape, only distorted by the way a guitar is tuned (in standard tuning, that is).
We know that a guitar is tuned in fourths except for the second string that is tuned a major third above the third string (G to B). This enables us to have the first and sixth string tuned to the same note and simplifies the fingerings of chords and scales since we just have four fingers to use but it distorts every chord and scale shape when they cross the second/third string .
If all the strings were tuned in fourths the shapes would look the same but we would need extra fingers to play them so we have to compromise but, knowing a few rules, we can easily move our shapes across the strings and approach the study of chords and scales in a different way.
I called these rules 'The Laws of Fretmapping' and they are the subject of another course, for now we'll just consider the first one:
“When moving a shape across the strings on a standard tuned guitar you move up one fret when you go from the third to the second string and you go back one fret when move from the second to the third.”
Let's see it in action starting from the E shape: