Musical Intervals - Scales Vs. Chords Options

[The Professor]

Musical Interval Lingo

One of the most common questions I get when it comes to talking about notes and intervals is, “How come a 2nd and 9th are the same thing, and when do I say 9th and when do I say 2nd?”

To help answer these questions, here is a short primer on intervals when it comes to scales vs. chords, which should help tackle any issues when it comes to using different names for the same interval in any given key.


The short answer is that when you are talking about scales you use the numbers 1 to 8 for each note in the scale, so a C major scale would be 1-2-3-4-5-6-7-8.

Then, you use the numbers up to 13 when talking about chords. So, the notes of C major expressed as a chord in numbers are 1-3-5-7-9-11-13.

Since scales are built in steps and use step-wise motion, we use ordered numbers, from 1 to 8, to talk about those notes.

But, as chords are built in thirds, in that you stack every 2nd note on top of each other to produce the chord, we use stacked numbers from 1 to 13 to talk about the notes of a chord.


Here is an example of a C major scale written as both a scale and as a chord, with the corresponding numbers below each note.






As you can see, the numbers 1-3-5-7 line up to the same notes in either case. But, 2 and 9, 4 and 11 and 6 and 13 are the same notes but different numbers.

This means that if you are talking about the note D in the C major scale you would call it a 2nd, but if you were talking about the note D in a C chord you would call it a 9th, the smaller number is used for the scale the larger number for the chord.

So there is the short answer to the question, if you are talking scales use the numbers 1-8, if you are talking chords use the numbers 1-13.

If you want to dig into these concepts further, here are some articles for further reading that you can explore in your own study.

Theory Quick Start Guide

Musical Intervals For Guitarists

Mastering Major Scales for Guitar

Mastering Guitar Chord Theory

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