With Part Four, Spinoza's Ethics finally earns the right to its title and enters the domain of moral philosophy, understood in the classic sense as an investigation into human well-being and the good life. Having laid the proper metaphysical, epistemological, and psychological foundations, and having established his essential claims about Nature and the place of the human being within it with geometric necessity, Spinoza can now begin his analysis and assessment of how human beings ordinarily pursue their lives, with a view ultimately toward discovering a remedy for the things that ail them and keep them from approaching human perfection.

The results of this analysis are not pretty, as the title of Part Four – “On Human Bondage, or the Powers of the Affects” – might suggest. For the most part, human beings live lives directed by the passions, not by reason. With our desires led about by pleasure and distracted by pain, we pursue transitory, false goods (such as material possessions, honor, and mundane power) and place our happiness in securing them, all the while ignoring the more permanent and valuable true good that, albeit with some effort, is within everyone's grasp, viz. knowledge and understanding. Spinoza is intimately acquainted with the life whereof he speaks, since he himself was once in its throes. It was only his disillusionment with the values embodied in such a life that made him turn to philosophy and the search for true happiness.