An interval is the distance in pitch between two notes. It can be measured by the number of scale steps or by the exact number of semitones. Intervals are described as major, minor, perfect, augmented, or diminished according to their size and quality.

Melodies are sequences of intervals; chords are stacks of them. The ear recognizes intervals even when the absolute pitches change. Training the ability to identify intervals by ear is a fundamental part of musicianship because it allows musicians to understand and reproduce music accurately.

Some intervals feel stable and consonant; others feel tense and dissonant. Composers exploit those qualities to create motion and resolution. On instruments the physical distance between notes may or may not match the aural interval, depending on the tuning system and the instrument’s design.

• Distance between two pitches
• Described by size and quality
• Building block of melody and harmony
• Trained by ear in musicianship classes