The Problems of Philosophy advances an epistemological theory and a discussion of truth. Bertrand Russell uses an analytic method to make distinctions concerning our judgments about reality. He employs Cartesian radical doubt in the beginning as he concentrates on our knowledge of the physical world. Claiming certain beliefs about the table in his room, he wants to know if he really has any kind of knowledge through his beliefs and, if so, what kind of thing is the table. He reasons that the table consists of matter and that there is a method by which he can have knowledge of it. Seeing the table involves an awareness of something, a patch of brown that is oval. He calls this something a "sense-datum." It is not the sensation, but what the sensation is of. We take the sense-data to be signs of the existence of physical objects. From the experience of sense-data, we practice a rational process of inference to get to the physical world.

In opposition to idealism, the view that "whatever can be known to exist, must be in some sense mental," Russell defends the reality of both universals and particulars. Universals are what particulars exemplify. Particulars are physical objects and are in one place at a given time. Universals include qualities, like whiteness, or relations, like "being to the left of." Russell allows for spatial, temporal, and causal relations. Since idealists take everything to be mental, Russell thinks that they confuse the "act" of sensation with the "object" of sense-data.

Russell believes that he has knowledge of his patch of sense-data by acquaintance and that he has knowledge of the signified physical object, the table, by description. He develops a distinction between knowledge by acquaintance and knowledge by description. He holds that we have immediate acquaintance only with our sense-data, and we therefore have direct knowledge. On the theory of descriptions, there are two kinds of terms that we use for an object, its name and definite descriptions. Russell's chief example, later, is "Bismarck" or "The first Chancellor of the German Empire." Employing descriptions enables us to think about and understand objects with which we have no acquaintance. We can thereby have indirect knowledge of things.

Russell is generally supportive of our natural inclinations and accounts for intuitions in his theory of truths. The major logical constructions intrinsic to Russell's theory are facts, propositions, and complexes consisting of universals and particulars. Facts exist much as we would ordinarily imagine—they are independent of human awareness. Particulars and universals are related together in propositions. A proposition is a complex philosophical expression of meaning. Russell's usage usually associates propositions as statements about objects and their relations. A proposition can constitute knowledge if it is appropriately arranged with universals and particulars. Russell makes this type of arrangement clear, though it can be technically challenging. On the theory that Russell develops, a true proposition is a correspondence between a belief and a fact.

Russell also gives a meaningful account of a priori knowledge. He advocates a Platonic attitude toward universals, which are like Platonic "ideas." Arguing that it is possible to have acquaintance with a universal without knowing of a single instance of that universal, the possibility of a priori knowledge becomes comprehensible. We can also have knowledge of general principles seeming to have the same degree of certainty as knowledge derived from our own experiences.

The Problems of Philosophy provides an overview of major philosophical achievements. Russell critically analyzes older arguments and responds to them equipped with his own set of distinctions and apparatus. The context of problems that arises is universal, however, and what interests us about reality and our knowledge of it is constant.

Russell's dialogue in this book proposes a forum for direct address and discussion. Though Russell is the only character present in the discussion, and his voice modulates between the informed philosopher interlocutor and the curious man on the street. He enlists his readership in a declarative "we." Russell employs a mouthpiece that both smoothes the difficult transitions between ideas and repeatedly subjects them to a built-in critical voice. He promotes a persistent mode of questioning familiar to the philosophical discipline, which structures much of the discussion. Each chapter builds on previous ideas and prepares for the progress of more developed ideas. Therefore, it is a very good idea to progress with his discussion, in order.