In music theory, a diatonic scale (or heptatonia prima) is a scale composed of seven distinct pitch classes. The diatonic scale includes five whole steps and two half steps for each octave, in which the two half steps are separated from each other by either two or three whole steps, depending on their position in the scale. This pattern ensures that, in a diatonic scale spanning more than one octave, all the half steps are maximally separated from each other (i.e. separated by at least two whole steps). The word "diatonic" comes from the Greek διατονικός, meaning progressing through tones.