# What an interval is

*Module 4 · Lesson 1: Intervals · BazzLow*

> Measure an interval in two ways, by letter names and by semitones.

Before this lesson: [1.4 The chromatic scale](https://bazzlow.com/en/notes-and-fretboard/chromatic-scale/)

Almost everything in theory is built from one idea: the distance between two notes. That distance is called an interval, and you can measure it in two different ways.

## What an interval is

An **interval** is the distance in pitch between two notes. If you play one note after the other, it is a **melodic interval**; if you play both together, it is a **harmonic interval**. An interval can go up (ascending) or down (descending). It can start on any note, not only on the first note of a scale: E→B is an interval too.

Every interval has a **number** and a **quality**. This lesson is about the number; the quality comes in lesson 4.2.

## The number: count the letters

The **interval number** counts letter names, **including both ends**:

- C→E covers C D E: a **3rd**;
- C→G covers C D E F G: a **5th**;
- C→C an octave higher is an **octave** (an 8th);
- C→C on the same pitch is a **unison** (a 1st).

Because both ends are counted, two 3rds stacked make a 5th, not a 6th: C–E plus E–G is C–G.

## The size: count the semitones

The **semitone count** says exactly how big the interval is. On the bass, that is the number of frets. C→E is 4 semitones; C→E♭ is 3. Both are 3rds, because the letters are the same, but they are different intervals. The quality, in the next lesson, names that difference.

> **Diagram:** One string, the A string. From C at fret 3: a 3rd above is E at fret 7 (letters C D E, 4 semitones); a 5th above is G at fret 10 (letters C D E F G, 7 semitones).

## Try it

On the A string, from C (fret 3), play the note a 3rd above, then a 5th above. Count the letters out loud, then the frets.

## New terms

- interval
- melodic interval
- harmonic interval
- unison
- interval number

Page: https://bazzlow.com/en/intervals/what-is-an-interval/