A video tutorial I have seen speaks of an unprepared and unresolved double leap.
Can someone explain what this is please?
In first species counterpoint all intervals must be consonances; specifically, they must be major or minor thirds/sixths or perfect fifths/octaves.
The example in the video is:
The narrator has written this as an error-detection exercise; students are to find the errors that she has intentionally written in.
I've made red the particular error that she's discussing when she says "an unprepared and unresolved double leap." You'll notice that the F up to B♭ is a P4, which is considered a dissonance in this style and thus not allowed in first species counterpoint.
When she says this F to B♭ perfect fourth is unprepared and unresolved, she's really using terminology you'll learn later. In later species, you'll learn that almost all dissonances are prepared (or "approached") and resolved (or "left") by step. The soprano line here is neither approached nor left by step, but rather by a leap on either side; thus it's "an unprepared and unresolved double leap."
Unfortunately for the narrator, she made a pretty big error in the video: she lists the A up to D in m. 5 as a major sixth, but it's actually a P4 (which you know is not allowed in first species). This makes the red error even worse, because know we see she's approaching that P4 dissonance from another P4 dissonance.