After finding an interval's size, we will eventually need to find its quality. Interval quality has different possibilities depending on the size of the interval. For unisons/primes, fourths, fifths, and octaves, there are three possibilities: perfect, augmented, or diminished. For seconds, thirds, sixths, and sevenths, there are four possibilities: major, minor, augmented, or diminished. As you probably noticed, the big difference between these two sets of intervals is that some can be called perfect, while others can be called major or minor. Before we begin analyzing quality for intervals, we need to make sure we have these two quality categories memorized: