Enter Simon Blackburn, moral philosopher and former Professor of Philosophy at both Cambridge University and the University of North Carolina Chapel Hill. Where Ayer and Garrett cannot strike all three cords with their books, Blackburn does so with his book How to Read Hume. While his book is only 106 pages from cover to cover (Ayer's is 117 and Garrett's is 348), Blackburn manages to cover adequately Hume's views on epistemology, causation, natural religion, aesthetics, personal identity, and moral theory. Even more impressive, one does not need to take a class in philosophy to understand what Blackburn is saying, because he simplifies things down to the understanding of a novice while still remaining able to keep things interesting for the person who is well read in Humean thought.
There are some problems with Blackburn's book, however. The main problem is that Blackburn makes no point to remain objective; he declares from beginning to end that he is a fan of Hume and his thought (which is unnecessary considering anyone who has ever read Blackburn knows that Hume is his idol. Take these two quotes for instance from the very beginning of the book and the very end of the book:
"Hume is the greatest British philosopher. But he is also the most misunderstood. In this short book I hope to help the reader to understand how both these things can be true, for it is only when we work through the things that make Hume perplexing that we discover the things that make him great."
"On all the topics that we have considered, he is either the most profound thinker of the modern world, or if not, then at least occupies the very front rank."While it may be true that Hume is one of the greatest philosophers of all time (very few philosophers, especially in the western analytic tradition would disagree), this is something that the reader should find out for themselves rather than having it thrust upon them. Blackburn's personal biases also come through when he talks about Hume and natural religion, which may be unsurprising considering that Blackburn is a former vice president of the British Humanist Association.
Do not get the impression that I do not like Blackburn's book, because that is not the case. I merely am pointing out that the biases can get it the way of what he is trying to accomplish, which is getting readers introduced to Hume's thought, not Blackburn's interpretation of Hume's thought, no matter how brilliant and well written it may be.
The brightest part of the book is probably Blackburn's treatment of Hume's moral theory, showing how morality, while subjective, can still be studied and put into a program that is liveable for all human beings. Also, his "Science of Man" chapter is also well done, and is of the upmost importance because that was the totality of Hume's project, whether he was talking about causality or taste; Hume strove to understand human nature in a way that would make all other disciplines make sense, and he did a very good job of it.
If one is looking for a brief introduction to Hume's thought before tackling the Treatise, I highly recommend Blackburn's book to you. It can be read in a few hours, has good depth, is well written, and will prepare a person (whether expert or novice) to tackle Hume's thought head on.