Hume begins the "Enquiry" by saying that there are two kinds of philosophical thinking. The first is "easy and obvious philosophy" and the second is "accurate and abstract philosophy". He describes the first as being written in a poetic style and that it uses examples from everyday life so we can see the difference between right and wrong.He says that this type of philosophy is popular and follows from common sense, therefore there are rarely errors in it.
The second philosophy, accurate and abstract philosophy, does not direct our behavior. Instead, it focuses on what causes that behavior and why we do the things we do and uses abstract reasoning to attempt to make sense of it. He says that since this area of philosophy does not use common sense, errors are made often and because of this, this area is sometimes rejected.
Hume goes on to say that the best objection against A&A philosophy is that it is a confused attempt to explain what we don't know by blind prejudice. Hume's reply to this is that this should be more reason for us to study it closely.