Getting Started
Music is composed of pitches organized in time. The most fundamental relationship between any two pitches—whether played together to form harmony or one after another to create a melody—is the interval. Mastering the identification and description of intervals is the foundational skill upon which all analysis of harmony, melody, and counterpoint is built.
What You Should Be Able to Do
Identify by size and quality any harmonic or melodic interval presented in musical notation.
Describe by size and quality the intervals heard between pitches in performed music.
Distinguish between melodic steps and leaps in a musical line.
Notate a specified interval above or below a given pitch.
Define the five interval qualities and know which apply to which interval sizes.
Key Concepts & Analysis
The analysis of intervals is a precise process of measurement. Every interval has two essential components—its size and its quality—which together provide a complete description of the distance between two pitches.
The Two Components of an Interval: Size and Quality
An interval is defined as the distance in pitch between two notes. To describe an interval completely, we must state both its numerical size (e.g., second, third, fifth) and its modifying quality (e.g., major, minor, perfect). Stating "a third" is incomplete; stating "a major third" is a complete and unambiguous description.
The five qualities used to describe intervals are perfect, major, minor, augmented, and diminished. The specific quality an interval can have depends on its size.
Determining Interval Size (The Number)
The size of an interval is found by counting the number of letter names spanned by the two notes, inclusive of the starting note. This is done by treating the lower note as "1" and counting each successive letter name up to the higher note.
Example 1: From C up to G.
Count the letter names: C (1), D (2), E (3), F (4), G (5).
The size is a fifth.
Example 2: From F up to B-flat.
Count the letter names: F (1), G (2), A (3), B (4).
The size is a fourth, regardless of the flat accidental.
Accidentals (sharps, flats, naturals) do not change the numerical size of an interval. For example, C to G, C to G-sharp, and C to G-flat are all types of fifths. The accidentals only affect the interval's quality.
Determining Interval Quality (The Modifier)
After finding the size, the quality is determined by measuring the precise distance in half steps or by relating the upper note to the major scale of the lower note. Intervals are divided into two families based on the qualities they can take.
The Perfect Family:
Unisons, fourths, fifths, and octaves are classified as perfect intervals in their most stable, diatonic form.
A perfect unison (P1) is the same note (0 half steps).
A perfect fourth (P4) is 5 half steps.
A perfect fifth (P5) is 7 half steps.
A perfect octave (P8) is 12 half steps.
The Major and minor Family:
Seconds, thirds, sixths, and sevenths are classified as either major or minor in their common diatonic forms. The simplest way to determine the quality is to use the major scale of the lower note as a reference. If the upper note is a diatonic member of the lower note's major scale, the interval is major (or perfect).
Example: C up to E
Size: C(1)-D(2)-E(3). It is a third.
Quality: In the key of C major, the note E is the third scale degree (^3). Therefore, the interval is a major third (M3).
Example: C up to E-flat
Size: C(1)-D(2)-E(3). It is a third.
Quality: The major third above C is E. The note E-flat is one half step smaller than E. An interval that is one half step smaller than a major interval is a minor third (m3).
Augmented and Diminished Qualities:
These qualities arise when an interval is expanded or contracted by a half step from its perfect or major/minor state.
An augmented interval is one chromatic half step larger than a perfect or major interval.
- C to G-sharp is an augmented fifth (A5), as it is a half step larger than the perfect fifth (C to G).
A diminished interval is one chromatic half step smaller than a perfect or minor interval.
C to G-flat is a diminished fifth (d5), as it is a half step smaller than the perfect fifth (C to G).
B to F is a diminished fifth (d5). In B major, the perfect fifth is F-sharp. F-natural is a half step smaller.
C to E-double-flat is a diminished third (d3), as it is a half step smaller than the minor third (C to E-flat).
Harmonic vs. Melodic Intervals
The context in which an interval appears determines its classification as either harmonic or melodic.
A harmonic interval describes the distance between two pitches that are sounded simultaneously. It is a vertical measurement, fundamental to the concept of harmony and chords.
A melodic interval describes the distance between two pitches that are sounded in succession. It is a horizontal measurement, fundamental to the shape and character of a melody.
Steps and Leaps in Melodic Motion
Melodic intervals are further categorized by their general type of motion.
A step is a melodic interval that traverses adjacent pitches of neighboring letter names. This refers to any type of second (major, minor, or augmented). Motion by step is also called stepwise or conjunct motion.
A leap is a melodic interval that is larger than a step. This includes all thirds, fourths, fifths, and larger intervals. Motion by leap is also called skip or disjunct motion.
Data & Organization Tools
The following table summarizes the relationship between interval families and their qualities. The "Base" quality refers to the diatonic form found in a major scale starting on the lower note.
| Interval Size | Base Quality | One Half Step Smaller | One Half Step Larger |
|---|---|---|---|
| Unison, 4th, 5th, 8ve | Perfect | Diminished | Augmented |
| 2nd, 3rd, 6th, 7th | Major | minor | Augmented |
| 2nd, 3rd, 6th, 7th | minor | Diminished | Major |
Evidence Bank
Interval: The distance in pitch between two notes.
Size: The numerical distance between two letter names, counting the first as "1" (e.g., a 2nd, 3rd, 4th).
Quality: The modifier describing an interval's exact distance and sonority (Perfect, Major, minor, Augmented, or Diminished).
Harmonic Interval: Two pitches sounded at the same time, creating a vertical alignment on the staff.
Melodic Interval: Two pitches sounded in sequence, creating a horizontal distance in the score.
Step: A melodic interval of a second, moving from one letter name to the next (e.g., G to A). This is the basis of conjunct motion.
Leap: Any melodic interval larger than a second (e.g., C to E). This is the basis of disjunct motion.
Perfect Intervals: The most stable intervals: unisons, fourths, fifths, and octaves.
Major/minor Intervals: The intervals with two common diatonic forms: seconds, thirds, sixths, and sevenths.
Skill Snapshots
Notational Skill: To identify the interval from D up to F-natural: first, count the letter names D(1)-E(2)-F(3) to determine the size is a third. Second, reference the D major scale (which contains F-sharp). The note F-natural is one half step lower than the major third (F-sharp), so the quality is minor. The interval is a minor third (m3).
Aural Skill: The first two distinct pitches of the melody "Twinkle, Twinkle, Little Star" form an ascending perfect fifth (C-G). The first two pitches of the NBC chimes form a major sixth followed by a descending perfect fourth (G-E-C). Recognizing these common patterns in performed music is a key analytical skill.
Conceptual Skill: The qualities are related by half-step alterations. Making a major interval smaller by one half step creates a minor interval. Making that minor interval smaller by another half step creates a diminished interval. Conversely, making a major interval larger by a half step creates an augmented interval.
Common Misconceptions & Clarifications
Confusing Size and Quality: An interval must have both a number and a name. Describing C to E-flat as simply "minor" is incorrect; it is a "minor third."
Incorrectly Counting Size: Students often count the "gaps" between notes. The correct method is to count the first note as "1" and include every letter name. C to E is a third, not a second.
Forgetting the "Perfect" Family: Seconds, thirds, sixths, and sevenths can be major or minor. Unisons, fourths, fifths, and octaves are perfect. There is no such thing as a "major fifth" in standard terminology; it is a perfect fifth.
Enharmonic Confusion: An augmented fourth (e.g., F to B) and a diminished fifth (e.g., F to C-flat) may sound the same on a piano, but they are spelled differently and have different numerical sizes. Size is always determined by the letter names, not the sound alone.
Summary
An interval is the basic unit of measurement for the distance between any two pitches. A complete description requires both a numerical size (second, third, etc.) and a specific quality (perfect, major, minor, augmented, or diminished). Intervals can be harmonic (simultaneous) or melodic (successive). Melodic intervals are further classified as steps (seconds) or leaps (larger than a second), which provides the first layer of analysis for melodic contour. A fluent ability to identify, notate, and aurally recognize intervals is an essential prerequisite for the study of chords, voice leading, and musical analysis.