When a triad is formed by sounding three notes separated by thirds, it is said to be in root position. The lowest note is called the root, the middle note is the third, and the top note is the fifth.
Repositioning these notes by changing the octaves does not create a new chord. Instead, it produces an inversion. In the example below, each of the three chords has the notes C, E, and G. In all three chords, C is the root, E is the third, and G is the fifth.
The first chord is in root position. The second chord, where the lowest note is the third, is in first inversion. We indicate this with a small "6," which is the interval between the lowest note and the highest note. The third chord, where the lowest note is the fifth, is in second inversion. This is indicated by adding a small "6" and "4," the two intervals from the lowest note to the others.
A chord with more than three notes (such as a 7th chord, which we will study later) has more than three inversions. In the example above, the root position chord consists of root C, third E, fifth G, and seventh B♭. The root position chord has a small "7" added. The first inversion chord, which once again has the third as the lowest note, is marked with a "6" and a "5," showing the intervals from the third up to the root and seventh. The second inversion chord again has the fifth on the bottom, and is marked with a "4" and a "3," again showing the intervals to the root and seventh.
Since this chord also has a seventh, the inversion with the seventh in the bass is the third inversion, marked with a "4" and a "2," the intervals from the lowest note to the third and root.
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