The philosopher Aristotle wrote extensively about "first philosophy," giving it two definitions: "being as such" and "first causes." Although he did not coin the term metaphysics, his 14 books on this subject were gathered in the text Metaphysics. This book is considered one of the foremost authorities on the subject.http://plato.stanford.edu/entries/metaphysics/

• Aristotle - "The first philosophy (Metaphysics) is universal and is exclusively concerned with primary substance. ... And here we will have the science to study that which is, both in its essence and in the properties which, just as a thing that is, it has."
• Benedictus de Spinoza - "the logic of One Infinite Substance; No two or more substances can have the same attribute and it appertains to the nature of substance that it should exist. It must therefore exist finitely or infinitely. But not finitely. For it would then be limited by some other substance of the same nature which also of necessity must exist: and then two substances would be granted having the same attribute, which is absurd. It will exist, therefore, infinitely."
• Immanuel Kant - "Natural science (physics) contains in itself synthetical judgments a priori, as principles. ... Space then is a necessary representation a priori, which serves for the foundation of all external intuitions."
• David Hume - "We then call the one object, Cause; the other, Effect. We suppose that there is some connection between them; some power in the one, by which it infallibly produces the other, and operates with the greatest certainty and strongest necessity." http://www.spaceandmotion.com/
• Bertrand Russell - "Although this may seem a paradox, all exact science is dominated by the idea of approximation. When a man tells you that he knows the exact truth about anything, you are safe in inferring that he is an inexact man"

1. The nature of metaphysics
2. The nature of being
3. The first causes of things
4. Things that do not change
5. Space and time (considered before Einstein)
6. Modality - the possibility and necessity of propositions and things
7. Mental vs. Physical relationship
8. Free will vs. Determinism http://www.ucl.ac.uk/~uctytho/dfwIntroIndex.htm
9. Material constitution and identity - does reducing something to its parts define it?http://plato.stanford.edu/entries/metaphysics/