Scepticism is the second approach to metaphysics that Kant considered an alternative to his ‘critical’ investigation. It is David Hume who plays the role of the paradigmatic representative of this viewpoint. I begin by analyzing three different readings of Kant’s understanding of Hume’s scepticism about causality. Hume’s scepticism is seen as posing a challenge to natural science and ordinary knowledge, as a problem that puts into question the possibility of general metaphysics, or as a ‘dialectical’ form of scepticism primarily directed against special metaphysics. I suggest that the first reading is implausible. I argue that the second and third readings are compatible once one distinguishes between the perspectives of transcendental philosophy and the critique of pure reason, respectively. Finally, I show that one objection that has been raised against the third reading can be silenced if we interpret Kant’s reading of Hume from the standpoint of his history of pure reason.

This chapter addresses the rise of psychology without a soul. There were scientific conceptions of psychology with a soul in the eighteenth century. Psychologies without soul followed from David Hume’s treatment of mental life. Lange coined the phrase, “psychology without a soul,” promoting a scientific psychology free of metaphysics. Soulless psychology emerged with psychology as a natural science in Newtonian terms. It also reflected debates over the distinction between the mental and the physical and the status of the “knower” in consciousness. The chapter includes debates over “psychology without a soul," and the development of an objective psychology in behaviorism. The new psychology without a soul triumphed by 1910, when Angell declared that the funeral for the soul had been held.

Socrates provides here an eschatological account that is thoroughly integrated into a novel cosmology. I argue that the Phaedo’s cosmology draws on and reflects the account of forms and ordinary objects that Socrates presented over the course of the Phaedo. The result is a distinctly Platonic account of the cosmos and the afterlife, one that treats the best parts of the cosmos as form-like and the worst parts as the source of flux. How we live now determines whether after death we will live in a more form-like or flux-like area; this dwelling, in turn, determines whether our souls are benefited or harmed in the afterlife. Since Socrates does not suggest in the Phaedo that any god is responsible for the cosmos, I argue that he avoids needing to explain why our souls can be harmed in the afterlife. In the secondary literature, this section of the dialogue is universally called “the myth,” which has led to treating the entirety of his account as having the same epistemic status. I argue instead that the account has five distinct stages, only the fifth of which Socrates calls a “myth” (muthos).

The theme of the essential activity of the mind provided the exciting intellectual setting that made a compelling case for psychology’s founding, and also gave rise to competing models of psychology. Structural or content psychology, championed by Wundt and Titchener, defined psychology as the experimental study of the data of immediate experience through the method of trained introspection. This natural science model sought to reduce the contents of consciousness to constituent elements of sensory origin. The restricted definition and ambiguous methodology led to challenges. Nevertheless, structural psychology secured recognition of psychology as a science, and Müller, Hering, and Ebbinghaus, attempted to modify structural psychology. Additionally, Mach and Avenarius bolstered the justification for psychology as a natural science. An alternative, described as a human science model, proposed more open definition and methodologies. Brentano’s act psychology stated that the phenomenological processes of psychological events are inseparable from the environment and consciousness. The works of Stumpf, Külpe, Dilthey and Bergson all fall into the human science model, but the lack of systematic theory reduced their successful competition with structural psychology. In many respects, the “founding” of modern psychology was a false beginning, and neither model established a lasting framework for psychology.

The chapter looks at the ways in which the analytic method adopted in Parts I and II, where Kant addresses the possibility of mathematics and natural science, bears on the status of metaphysics.The essay canvasses two possible accounts of how mathematics and science relate to metaphysics as a priori cognition – the ‘Necessary Conditions’ view, and the ‘Examples First’ proposal – and rejects each.Rather, Kant denies that metaphysics can be a science not because it fails to achieve the necessity that we find in mathematics and natural science, but instead because metaphysics does not amount to cognition at all.The analytic method Kant adopts does not lead to a quick rejection of metaphysics as not being something we in fact possess, but requires a subtler and more complex case to show that metaphysics cannot have any cognition of an a priori object, though it still has some other methodological value to offer.

This chapter places Kant’s conception of a priori laws within the framework of the legal metaphors. It introduces the relevant aspects of natural right theory and the notion of laws in the natural sciences as historical background to the legal metaphors. The main argument is that Kant’s notion of laws is embedded in his legal metaphors and his account of natural regularities as lawful also originates in the natural right framework. This serves as background to Kant’s account of the understanding as prescribing laws to nature and to thought. The background of Kant’s notion of laws in natural right and natural science shows how reason’s a priori laws are both descriptive of regularities in nature and prescriptive of valid judgements.