Different types of motion between two voices

There are four main types of motion that are possible between two voices as summarised in the table below. In most tonal styles, any succession of intervals can appear in oblique or contrary motion but there are often restrictions on parallel or similar motion to a perfect intervals - i.e. perfect fifths, fourths and octaves.

Parallel - the two voices move in the same direction by the same interval
Similar - the two voices move in the same direction but by different intervals
Oblique - one voice stays stationary while the other moves
Contrary - the two voices move in opposite directions