This introduction presents the book's project: to expose issues with the question "why?"; to indicate the diversity of answers; and to explain the notion of a "grammar of why." It sets forth the three domains of why—the causes, the justifications of beliefs, and the goals—and then argues that the limits of this question, as well as the transgression of boundaries between kinds of "because," raise metaphysical issues.

This chapter considers why-questions related to facts or events and to beliefs. It disentangles those two kinds of reasons, and reflects on what a "good reason" for a belief means and on the limits of relying exclusively upon evidence when assessing beliefs. It also analyzes the concept of causation in ordinary discourse, and discusses skeptical objections to this concept.

This chapter investigates questions of why in the sciences. It considers the classical account of scientific explanation in terms of deduction from laws and facts, and its flaws. It then turns to an alternative account that sees explanations as causes. Finally, it argues that not all explanations are causal, and introduces "structural explanations" as an alternative answer to why-questions that are mostly mathematical.

This chapter considers why people act as they do. It presents the reasons for actions as structured in terms of beliefs and desire, distinguishing between a reason and a good reason to act. It shows how this why-question can be understood in terms of microeconomics, resorting to the notion of maximization of utility by rational agents. Thus it can be inferred that rationality should always be presupposed when dealing with other people, or considering actions done by people in the past, even though it is just a weak form of rationality. Finally, Spinoza's radical and seminal critique of the illusions of purposes outside of us is discussed.

This chapter explains why a conflation between cause and purpose when it comes to living beings is not illegitimate—and the answer relies on Darwinian biology. Functions are interpreted in terms of natural selection. It concludes with a discussion of the question "why life?" and emphasizes epistemic problems about the notion of life.

This chapter tackles how the discourse of history explains events that are at the same time stemming from natural, often random facts and human intentions. Herein is presented a theory of degrees of necessity of events that uses Lewis's "possible worlds" theory (although without being committed to his modal realism). This makes sense of the possibility that something can appear at the same time inexorable and contingent.

This chapter explains that one major illusion regarding "why?" consists in taking a structure of possible worlds characteristic of contingent events as a structure typical of inexorable events—and this fallacy relies on the assumption that contingent cause-and-effects relationships are grounded in a necessary relation of intentional nature, like God's will, destiny, and so on. It is shown how such fallacy originates from some properties of the narrative activity, which is rooted in human experience.

This chapter sees conspiracy theories as good examples of an attempt to search for reasons, where in fact there are none, because things happened by chance. A few motivations behind conspiracy theories are examined, and a general account of chance as a poorly unified concept is proposed.

This chapter relies on Romeo and Juliet's love story as an example of singular emotional facts that at the same time are there for a reason and seem to bypass causes, justifications, and intentions. It explains the relation between illusions of destiny and these singular events, which pertain to a dimension explored by novelists rather than philosophers, and which is labeled here (as many others have labeled it) as subjectivity.

The question "Why am I me?" seems to require an answer too obvious ("I'm me because 'I' is me!") to be an explanation. Yet, here it is claimed that, under some metaphysical assumptions, this question can be a legitimate question, likely to be answered by stating some matters of fact; whereas in the most common metaphysical frameworks, it is not a sound question.

This conclusion wraps up various claims asserted throughout the book. It indicates how metaphysics bears upon the bounds of sense surrounding the question "why?", and that ultimately these bounds depend upon the choice of one metaphysics over another. It then situates the book's overall account of "why?" within the metaphysical and epistemological controversies between dogmatism and skepticism or pragmatism.