What is the difference between a past and a present participial phrase? And what is a gerund? Now I can answer these questions confidently. What made me learn it was that the book keeps things simple—you learn clear rules without a lot of exceptions. I think the most important part was the mastery exams. This is where you have to know certain material (like memory sentences) before taking the test. I did get some zeros, but now I really know the material.