Books I–VI: Alpha, little Alpha, Beta, Gamma, Delta and Epsilon
- Book I or Alpha begins by discussing the nature of knowledge and compares knowledge gained from the senses and from memory, arguing that knowledge is acquired from memory through experience.[6] It then defines "wisdom" (sophia) as a knowledge of the first principles (arche) or causes of things. Because those who are wise understand the first principles and causes, they know the why of things, unlike those who only know that things are a certain way based on their memory and sensations. The wise are able to teach because they know the why of things, and so they are better fitted to command, rather than to obey. He then surveys the first principles and causes of previous philosophers, starting with the material monists of the Ionian school and continuing up until Plato.
- Book II or "little alpha": Book II addresses a possible objection to the account of how we understand first principles and thus acquire wisdom, that attempting to discover the first principle would lead to an infinite series of causes. It argues in response that the idea of an infinite causal series is absurd, and argues that only things that are created or destroyed require a cause, and that thus there must be a primary cause that is eternal, an idea he develops later in Book Lambda.
- Book III or Beta lists the main problems or puzzles (aporia) of philosophy.[7]
- Book IV or Gamma: Chapters 2 and 3 argue for its status as a subject in its own right. The rest is a defense of (a) what we now call the principle of contradiction, the principle that it is not possible for the same proposition to be (the case) and not to be (the case), and (b) what we now call the principle of excluded middle: tertium non datur — there cannot be an intermediary between contradictory statements.
- Book V or Delta ("philosophical lexicon") is a list of definitions of about thirty key terms such as cause, nature, one, and many.
- Book VI or Epsilon has two main concerns. The first concern is the hierarchy of the sciences: productive, practical or theoretical. Aristotle considers theoretical sciences superior because they study beings for their own sake—for example, Physics studies beings that can be moved[f]—and do not have a target (Telos (τέλος), end or goal; τέλειος, complete or perfect) beyond themselves. He argues that the study of being qua being, or First Philosophy, is superior to all the other theoretical sciences because it is concerned with the ultimate causes of all reality, not just the secondary causes of a part of reality. The second concern of Epsilon is the study of "accidents"[g], those attributes that do not depend on (τέχνη) or exist by necessity, which Aristotle believes do not deserve to be studied as a science.
Books VII–IX: Zeta, Eta, and Theta
Books Zeta, Eta, and Theta are generally considered the core of the Metaphysics. Book Zeta (VII) begins by stating that "being" has several senses, the purpose of philosophy is to understand the primary kind of being, called substance (ousia) and determine what substances there are, a concept that Aristotle develops in the Categories.[8] Zeta goes on to consider four candidates for substance: (i) the 'essence' or 'what it is to be' of a thing (ii) the universal, (iii) the genus to which a substance belongs and (iv) the material substrate that underlies all the properties of a thing.
- He dismisses the idea that matter can be substance, for if we eliminate everything that is a property from what can have the property, such as matter and the shape, we are left with something that has no properties at all. Such 'ultimate matter' cannot be substance. Separability and 'this-ness' are fundamental to our concept of substance.[9]
- Aristotle then describes his theory that essence is the criterion of substantiality.[h] The essence of something is what is included in a secundum se ('according to itself') account of a thing, i.e. which tells what a thing is by its very nature. You are not musical by your very nature. But you are a human by your very nature. Your essence is what is mentioned in the definition of you.
- Aristotle then considers, and dismisses, the idea that substance is the universal or the genus, criticizing the Platonic theory of Ideas.[i]
- Aristotle argues that if genus and species are individual things, then different species of the same genus contain the genus as individual thing, which leads to absurdities. Moreover, individuals are incapable of definition.
Finally, he concludes book Zeta by arguing that substance is really a cause.[j][10]
Book Eta consists of a summary of what has been said so far (i.e., in Book Zeta) about substance, and adds a few further details regarding difference and unity.
Book Theta sets out to define potentiality and actuality. Chapters 1–5 discuss potentiality,[k] the potential of something to change: potentiality is "a principle of change in another thing or in the thing itself qua other."[l] In chapter 6 Aristotle turns to actuality. We can only know actuality through observation or "analogy;" thus "as that which builds is to that which is capable of building, so is that which is awake to that which is asleep...or that which is separated from matter to matter itself".[11] Actuality is the completed state of something that had the potential to be completed. The relationship between actuality and potentiality can be thought of as the relationship between form and matter, but with the added aspect of time. Actuality and potentiality are distinctions that occur over time (diachronic), whereas form and matter are distinctions that can be made at fixed points in time (synchronic).
Books X–XIV: Iota, Kappa, Lambda, Mu, and Nu
- Book X or Iota: Discussion of unity, one and many, sameness and difference.
- Book XI or Kappa: Briefer versions of other chapters and of parts of the Physics.
- Book XII or Lambda: Further remarks on beings in general, first principles, and God or gods. This book includes Aristotle's famous description of the unmoved mover, "the most divine of things observed by us", as "the thinking of thinking".
- Books XIII and XIV, or Mu and Nu: Philosophy of mathematics, in particular how numbers exist.
