Perfect Intervals (4th, 5th)
Fourths, fifths, octaves and unisons get called “perfect” instead of major or minor. It's an inherited name, not a compliment — these intervals are identical in major and minor keys, so there's no second version to tell apart.
Why it matters
It's why a power chord fits over almost anything: root plus perfect fifth, with no third in it, so it commits to neither major nor minor. “Perfect” here means neutral, not better.
Used in a sentence
Digging deeper
Unisons, fourths, fifths and octaves get called “perfect” rather than major or minor. It is an inherited name, not a grade — these intervals are identical in major and minor keys, so unlike thirds and sixths there is no second version of them to distinguish.
Common questions
Why does a power chord sound neither happy nor sad?
Because it's a root and a perfect fifth with no third in it. The third is the note that decides major or minor, so leaving it out lets the chord sit over either — which is exactly why rock guitarists lean on it so hard.
Is there such a thing as an imperfect interval?
Not by that name. The intervals that aren't perfect — seconds, thirds, sixths and sevenths — are called major or minor instead, because each of them has a wider and a narrower version.
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