Chapter 5: Knowledge by Acquaintance and Knowledge by Description​

Russell’s theory of knowledge distinguishes between knowledge of things and knowledge of truths. Within knowledge of things, he differentiates between knowledge by acquaintance and knowledge by description. Knowledge by acquaintance is direct and non-inferential, such as perceiving a color or texture, whereas knowledge by description is indirect, relying on sense-data and inference to refer to objects beyond immediate experience.
Acquaintance forms the foundation of all knowledge, extending beyond sense-data to include memory, which allows us to retain awareness of past experiences, and introspection, which provides direct awareness of internal states like emotions and desires. Russell also considers the possibility of acquaintance with the Self, though he regards it as uncertain and ambiguous.
Knowledge by description plays a crucial role in how we understand the world and communicate, particularly when referring to objects and people we have never directly encountered. Language depends on descriptions, as seen in the use of proper names, which implicitly rely on descriptive knowledge rather than direct acquaintance. Russell illustrates this with the example of Bismarck, explaining that while Bismarck himself had direct acquaintance with his own identity, others-whether friends or historians-only knew him through descriptive means. This highlights how knowledge by description allows us to engage with concepts beyond our immediate experience.
Russell further explores the distinction between particulars and universals, using the example of "the most long-lived of men." While this phrase assumes the existence of a specific person, it consists entirely of universals and lacks direct acquaintance, making it impossible to infer concrete details. In contrast, statements that combine particulars and universals, such as describing Bismarck as an astute diplomat, allow for meaningful judgments based on knowledge derived from direct or indirect acquaintance.
He concludes that knowledge by description ultimately depends on knowledge by acquaintance, as all meaningful propositions must consist of elements with which we are directly acquainted. This principle reinforces how indirect knowledge is structured upon direct experience.
Despite its innovative framework, Russell’s theory has faced criticism. Some argue that his definition of sense-data contradicts his knowledge by description theory, as it suggests the physical world is ultimately unknowable. This raises concerns that knowledge by description may not truly be knowledge at all, since it relies on inferential connections rather than direct experience. Critics also contend that his theory reduces reality to subjective representations, making our understanding of the external world indirect and uncertain. While his approach offers a structured epistemological framework, it challenges traditional views of knowledge and perception by emphasizing the limitations of direct experience.