A motif is an easy to recognise, short musical idea, which is used to generate new music in a composition. Using the similar motifs throughout a composition helps to “glue” it together, as a unified piece of music.
Usually, motifs are defined by their rhythm.
The most famous motif in classical music is probably the first four notes of Beethoven’s 5th Symphony. It comprises four notes – three repeated quavers (8th notes) moving down in pitch to a minim (half note):
This motif (with slightly altered melodic shapes, but with the same rhythm) is repeated throughout the movement.
A melodic sequence is section of music which is repeated at a different pitch.
In this simple sequence, notes 1-5 are repeated but each one is a scale-step higher. This is an example of a rising sequence, because the repetition is higher pitched. You can also find descending sequences, which move downwards in pitch.
Like the motif, the sequence is used as way to unify a piece – they can help to make sure that a composition is built from connected ideas, so that it does not sound random.
Sequences can be either exact or not exact. “Not exact” just means there are some minor differences, which don’t make change the overall feel of the segment of melody. Here, the sequence has a minor change on the second beat, for example.
Sequences which use the notes from the same key will have different interval qualities between the notes. In this example, the interval between notes 3 and 4 is a minor 2nd in the first example, but a major 2nd in the second example. This type of sequence is called tonal. If the intervals are kept exactly the same, the music will have to change key, and the type of sequence is called “real”.
Imitation happens when a section of music is repeated in a different part, or instrument, or pitch, straight away, as a kind of echo. In keyboard music, imitation could occur between the right- and left-hand staves, or even on a single stave which has been divided into a higher and lower part.
Here is an example of imitation from Saint-Saëns Clarinet Sonata (1st movement).
The piano has C-Bb-Ab, which is immediately echoed in the clarinet part at the same pitch (transpose down a major 2nd into concert pitch!)
Imitation can be melodic, which means the entire melody is copied (as above), or just rhythmic. In rhythmic imitation, the rhythm is copied but the melody notes are changed. Here, the flute and clarinet use the same rhythm, but the echo moves in a different melodic direction, and by a different interval: