The collection of intervals 1, 4, 5, and 8 are typically categorized as which type of intervals?

• A. Perfect intervals
• B. Major intervals
• C. Minor intervals
• D. Diminished intervals

Answer: (A)

In music theory, certain intervals are labeled as perfect, major, minor, diminished, or augmented. The set 1, 4, 5, and 8 corresponds to unison, a perfect fourth, a perfect fifth, and an octave. These are the intervals that maintain the “perfect” quality in their simple forms, and they sound especially consonant. They arise from exact, simple frequency ratios (unison 1:1, fourth about 4:3, fifth 3:2, octave 2:1). Major and minor apply to the other diatonic intervals (seconds, thirds, sixths, sevenths), while diminished and augmented describe altered versions of any interval. Because all of these shown intervals are the unison, perfect fourth, perfect fifth, and octave, they are categorized as perfect intervals.