Imagine that you're opening a series of closed doors with no knowledge of whether there is something behind each one. Just before you open the first door, you're probably thinking there's roughly a 50% chance that you'll find something or someone behind it, so you'll be half expecting that there is nothing behind it. Imagine that you open 5 doors and there's nothing behind any of them. You'll have a much higher expectation that there's nothing behind Door 6 because a pattern has been created. An Implied Pattern is being created and sets you up to expect a certain result behind each succeeding door that you open. Implied Patterns can be applied to the way that you compose music. You can setup Implied Musical Patterns and setup a listener with certain 'Musical Expectations' of what the next musical element(s) will be.
You create Musical Expectation by writing Musical Events which imply the next event before it occurs. For example, you could write a melody which uses only 1/8th notes in a constant pattern. The more this occurs, the more the listener will expect the next note to be an 1/8th note. An Implied Rhythmic Pattern of repeating 1/8th notes has now been created.
The variety of musical options to create these Implied Patterns is immense. For example, when you're writing a melody, you could write a series of notes that continuously get higher from the starting note (Ascending Melodic Shape). You could write each note in the melody so that it is always 4 semitones away from the preceding note (Disjunct Melodic Motion - see below) or you could write two concurrent melodies so that the notes of each melody always play at the same time and are always 7 semitones or a Perfect Fifth interval away from each other (Parallel Motion - see below). When programming drums, you could write a Kick drum that always plays on the downbeat of every bar (the classic 4/4 Kick) or a Clap that always plays on the 2nd and 4th beats of the bar (the classic Clap/Snare pattern). When writing a chord progression, you could always use chords in their Root Position (Root note on the bottom) or always start a 4 bar progression with the Tonic chord.
By creating Implied Patterns, the listener gets the impression that they can predict the next Musical Event before it occurs. You can induce a more relaxed state in the listener by constantly writing the expected Musical Event. Inversely, you can create surprise or shock if the expected Musical Event doesn't happen. In this way, you are now creating and manipulating Musical Expectation.
An example of Disjunct Melodic Motion:
An example of Parallel Motion