A minor second is one comprising one half-step. Ex. B—C.
A major second is one comprising two half-steps. Ex. B—C♯.
An augmented second is one comprising three half-steps. Ex. F—G♯.
187. A third is an interval comprising two seconds.
A diminished third has two minor seconds (i.e., two half-steps). C—E♭♭.
A minor third has one minor and one major second (i.e., three half-steps). C—E♭.
A major third has two major seconds (i.e., four half-steps). C—E.
188. A fourth is an interval comprising three seconds.
A diminished fourth has two minor and one major second. C♯—F.
A perfect fourth has one minor and two major seconds. C—F.