---
title: Intervals
category: Fundamentals
slug: intervals
related: [notes-and-pitch, scales, triads, fretboard-geometry]
url: https://fourthshub.com/docs/intervals
---

# Intervals

An **interval** is the distance between two pitches, measured in half steps.

## The 13 Simple Intervals

| Interval | Half Steps | Sound |
|----------|-----------|-------|
| Perfect Unison (P1) | 0 | Identity |
| Minor 2nd (m2) | 1 | Tense, dissonant |
| Major 2nd (M2) | 2 | Open, whole step |
| Minor 3rd (m3) | 3 | Sad, minor quality |
| Major 3rd (M3) | 4 | Happy, major quality |
| Perfect 4th (P4) | 5 | Stable, open |
| Tritone (TT) | 6 | Maximum tension |
| Perfect 5th (P5) | 7 | Strong, consonant |
| Minor 6th (m6) | 8 | Bittersweet |
| Major 6th (M6) | 9 | Warm, sweet |
| Minor 7th (m7) | 10 | Bluesy, dominant |
| Major 7th (M7) | 11 | Bright, leading tone tension |
| Perfect Octave (P8) | 12 | Same note, higher |

## Consonance and Dissonance

**Perfect consonances**: unison, octave, perfect 5th. These are the most stable intervals, anchoring harmony since ancient times.

**Imperfect consonances**: major and minor 3rds and 6ths. These define chord quality (major vs. minor) and form the basis of triadic harmony.

**Dissonances**: 2nds, 7ths, and the tritone. These create tension that demands resolution. The tritone (augmented 4th / diminished 5th) is the most unstable interval and drives dominant-to-tonic resolution.

## Compound Intervals

Any interval wider than an octave is **compound**. A 9th is an octave + a 2nd (14 half steps). An 11th is an octave + a 4th (17 half steps). A 13th is an octave + a 6th (21 half steps). These are critical in jazz harmony as chord extensions.

## Interval Inversion

Subtracting an interval from an octave gives its **inversion**. Major inverts to minor, perfect stays perfect, augmented inverts to diminished. A major 3rd (4 semitones) inverts to a minor 6th (8 semitones). The two always sum to 12.

## On the Guitar in P4

In fourths tuning, every interval has **exactly one shape** across any pair of adjacent strings. A major 3rd is always the same fret pattern regardless of where you play it. This is the fundamental geometric advantage of uniform tuning.