# Intervals, Music theory

The distance between any two notes

Intervals are the DNA of melody and harmony. Learn to identify the distance between any two notes by ear and by sight. This unlocks chord construction, ear training, and musical analysis.

Beginner · 4 lessons · approximately 50 minutes of material (not a mastery deadline).

## Free lesson sample: Distinguish a major third from a minor third

An interval has a number and a quality. Count letter names, including both endpoints, for the number. Then count semitones for the quality. You need both: two intervals can span the same letters but sound different.

Before you start: Compare ascending C4–E4 and C4–E♭4. Imagine a keyboard or write the notes down. Count the moves between pitches, not the number of keys including the starting note.

### The example, written out
- C4 → E4: letters C–D–E; semitones C–C♯–D–D♯–E.
- C4 → E♭4: letters C–D–E; semitones C–D♭–D–E♭.

### Try it step by step
1. Count the letter names for each interval. Both C–D–E sequences contain three letters.
2. Count the semitone moves: C to E takes four; C to E flat takes three.
3. Apply the same method to D4–F4 and D4–F♯4 before reading the worked answer.

### Worked answer
C–E is a major third (four semitones); C–E♭ is a minor third (three). D–F is a minor third and D–F♯ a major third. The accidental changes the quality without changing the interval number because the letter names still span a third.

### Common mistakes
- Do not count C as the first semitone move; moving from C to C♯ is one move.
- Do not name intervals by semitone count alone: note spelling also determines whether an interval is a third, fourth, or another number.

[Use major and minor thirds to build triads](/learn/theory/chords)
[Review whole steps, half steps, and scale spelling](/learn/theory/scales-keys)

## Before this module
- [Scales & Keys](/learn/theory/scales-keys), Half steps, whole steps, and the major scale

## What this module covers
1. **What Are Intervals?**, Measuring the distance between any two notes (10 min)
2. **Perfect Intervals**, Unisons, fourths, fifths, and octaves (14 min)
3. **Major, Minor & Perfect Intervals**, The exact size of every interval from unison to octave (14 min)
4. **Compound Intervals**, Intervals larger than an octave (12 min)

## What comes next
- [Chords & Harmony](/learn/theory/chords), Triads, seventh chords, and progressions

## Where should I start with intervals?
The curriculum places Scales & Keys before this module. Review those topics if they are unfamiliar. The first lesson is “What Are Intervals?”: Measuring the distance between any two notes. The order is a study guide, not proof that every learner needs the same pace.

## How long is the intervals module?
The 4 listed lessons total approximately 50 minutes of material. That estimate describes lesson content, not the practice time needed to become comfortable with the distance between any two notes. Revisit one task at a time and use feedback from a teacher where physical technique is involved.

## What can I try here without an account?
The complete “Distinguish a major third from a minor third” exercise, its worked answer and common mistakes are free on this page. The lesson list and linked public tools are also open. A free account includes the complete five-lesson foundation module in each instrument and five lessons in music theory, with saved progress and no expiry. Later lessons require the relevant paid package.

## Continue in Arco
The complete five-lesson foundation module in each instrument and five music theory lessons are free with an account, including saved progress and no time limit. Later lessons require the relevant paid package. Public samples do not assess your physical technique or certify exam readiness.

[See packages and pricing](/pricing) · [Back to the music theory curriculum](/learn/theory)

Canonical source: https://arcosounds.com/learn/theory/intervals