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Interval
TUTORZONE SUBJECT GUIDE · MUSIC THEORY
From the calm, stable perfect fifth to the restless minor second, intervals are the hidden building blocks of every melody, harmony and chord. This guide explains what an interval is, how it is named and measured, and why intervals matter for musical expression.
Direct Answer：What is an interval in music?
An interval is a hidden building block of melody, harmony, and chord; it is named and measured, from the stable perfect fifth to the restless minor。
What Is an Interval?
In music theory, an interval is the difference in pitch between two notes. This concept is crucial for understanding musical structure, melody, harmony, and chord construction. Intervals are typically described by their name, number, and duration.
An interval is simply the distance between two notes — the difference in pitch from one note to another. Intervals can be ascending (from a lower note to a higher one) or descending (from a higher note to a lower one). The length of an interval is determined by two factors: the number of notes (the length of the interval) and the pitch difference between the notes (a semitone or a whole tone).
Intervals are not only the distance between notes but also determine the emotional expression and atmosphere of music.
Types of Intervals: Classification by Size
Intervals can be divided into different types based on their size and nature. The size of an interval is determined by the pitch difference between two notes, and is usually described in terms of semitones (half-steps) or whole tones (whole-steps). By size, intervals fall into the following types:
Perfect Intervals
A perfect interval is a perfectly pitched interval between two notes that is completely stable and free of tension. They are the most common and harmonic intervals in music. Common perfect intervals include:
- Perfect Unison——Two notes that are exactly the same, such as two C notes.
- Perfect Fourth——For example, from C to F, or from G to C, there are 5 semitones between these two notes.
- Perfect Fifth——For example, from C to G, or from F to C, there are 7 semitones between these two notes.
- Perfect Octave——For example, from C to the C below or above, there are 12 semitones between the two notes.
Major Intervals
A major interval is a larger pitch difference between two notes, but it is not as stable as a perfect interval. Common major intervals include:
- Major Second——For example, from C to D, there is a gap of 2 semitones between these two notes.
- Major Third——For example, from C to E, there is a gap of 4 semitones between these two notes.
- Major Sixth——For example, from C to A, there are 9 semitones between these two notes.
- Major Seventh——For example, from C to B, there are 11 semitones between these two notes.
Minor Intervals
Minor intervals are usually a semitone shorter than major intervals, which can make them sound tense or unstable. Common minor intervals include:
- Minor Second——For example, from C to C#, there is a gap of 1 semitone between these two notes.
- Minor Third——For example, from C to E♭, there are 3 semitones between these two notes.
- Minor Sixth——For example, from C to A♭, there are 8 semitones between these two notes.
- Minor Seventh——For example, from C to B♭, there are 10 semitones between these two notes.
Augmented Intervals
Augmented intervals refer to raising the pitch of a basic interval by a semitone, making the interval wider. Common augmented intervals include:
- Augmented Second——For example, from C to D#, there is a gap of 3 semitones between these two notes.
- Augmented Fourth——For example, from C to F#, there are 6 semitones between these two notes.
- Augmented Fifth——For example, from C to G#, there is a gap of 8 semitones between these two notes.
- Augmented Seventh——For example, from C to B#, there are 13 semitones between these two notes.
Diminished Intervals
Diminished intervals are intervals that lower the pitch by a semitone, making the interval narrower. Common diminished intervals include:
- Diminished Second——For example, from C to D♭, there is a difference of 1 semitone between these two notes.
- Diminished Third——For example, from C to E♭♭, there is a gap of 2 semitones between these two notes.
- Diminished Fifth——For example, from C to G♭, there are 6 semitones between these two notes.
- Diminished Seventh——For example, from C to B♭♭, there are 9 semitones between these two notes.
Interval Degrees
Intervals can also be classified by degree — the number of note names between the two notes. For example, the interval from C to E is a third, and the interval from C to G is a fifth. Interval degrees usually start with the unison and are ranked by the number of notes.
| Degree | Example | Description |
|---|---|---|
| Unison | C to C | Two notes are identical, with no difference in pitch. |
| Second | C to D | The interval of 2 degrees. |
| Third | C to E | The interval of a 3rd. |
| Fourth | C to F | The interval of a 4th. |
| Fifth | C to G | The interval of a 5th. |
| Sixth | C to A | The interval of 6 degrees. |
| Seventh | C to B | The interval of a 7th degree. |
| Octave | C to C | An octave. |
How Intervals Shape Music
Intervals have many functions in music, mainly used in the following aspects:
- Melody Construction——Melodies are composed of notes of different intervals. The choice of intervals directly affects the melody’s flow, expression, and emotion.
- Harmonic Construction——A harmony is a chord formed by the simultaneous sounding of notes of different intervals. The choice of intervals in the harmony determines the color and tension of the chord.
- Chord Progression——The changes in a chord progression are based on changes in intervals. Changes in intervals can create chord transitions, giving the music a sense of flow and development.
- Emotional Expression——Different musical intervals can express different emotions. A larger interval (like a major third) can express openness or positive emotions, while a smaller interval (like a minor second) can express tension or instability.
Conclusion: Why Intervals Matter
Intervals are a core concept in music theory. They are not only the foundation of melody and harmony, but also key to musical expression. Understanding the sizes and types of intervals, as well as their application in music, helps musicians create richer, more harmonious music. Whether in composition, arranging, or performance, intervals are an indispensable tool, helping musicians understand and express the relationships between notes.
Frequently Asked Questions (FAQ)
Q: What is the difference between a semitone and a whole tone?
A semitone (or half-step) is the smallest pitch step on a standard keyboard — for example, C to C#. A whole tone is two semitones, such as C to D. Interval size is usually measured by counting these steps.
Q: How do major and minor intervals differ?
A minor interval is one semitone narrower than the corresponding major interval. For example, a major third spans 4 semitones (C to E), while a minor third spans 3 semitones (C to E♭) — which is why the two sound so different in mood.
Q: Why do perfect intervals sound stable while others sound tense?
Perfect intervals — the unison, fourth, fifth and octave — have simple frequency relationships and a very consonant, “settled” sound. Intervals such as the minor second or augmented fourth contain more dissonance, creating the tension that music then resolves into stability.
Q: How many semitones are in an octave?
A perfect octave spans 12 semitones — for example, from C up to the next C. This is the interval that divides the whole pitch system into repeating groups of notes.
Further Resources & Next Steps
- Official Resources——The Associated Board of the Royal Schools of Music (ABRSM) publishes graded music theory materials covering intervals and their notation.
- Further Reading——The AB Guide to Music Theory by Eric Taylor offers a clear, progressive introduction to intervals for students.
- Parent Tips——Practise recognising intervals by ear: play two notes on a piano or keyboard and ask your child whether the second is higher or lower, then whether the gap sounds wide or narrow.
Note: The information above is for reference only. Please consult professional education institutions for details.
This article was initially drafted and organised with AI. Editor / Professor Chan Kwok-wai; Managing Editor / Kong Yee-leung
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