What is meant by similar motion in music?

Similar motion in music refers to the concept of two or more musical lines or voices moving in the same direction, which can be either both ascending or both descending. This term is often used in the context of counterpoint and harmony, where composers may choose to move parts in similar motion to create a sense of cohesion or to maintain harmonic relationships.

When voices or instruments move in similar motion, the intervals between them may remain constant or change, leading to different harmonic textures depending on the prevailing intervals. This technique can enhance the overall sound and facilitate the development of harmony, while still allowing for distinct melodies.

Other options, such as playing different melodies simultaneously, creating parallel harmony with fixed intervals, or playing in unison, do not specifically describe the concept of similar motion and focus on different aspects of musical interaction or texture. Through similar motion, composers and performers can establish clear lines of melodic development while still emphasizing their relationship within the harmony.