How did Bertrand Russell and Ludwig Wittgenstein use sense data in their accounts of the physical world?

In the context of 20th-century analytic philosophy, Bertrand Russell and Ludwig Wittgenstein approached the relationship between experience and the physical world through the lens of logical atomism.1

Bertrand Russell and Sense Data

Russell utilized sense-data—the immediate objects of direct perception—to address how we gain knowledge of the external world. Because one can doubt the existence of physical objects (like a desk) but cannot doubt the occurrence of visual impressions, Russell argued that sense data are the only things we can name in a "strict logical sense".2

He proposed that physical objects are not directly perceived but are instead logical constructions built out of these private sense data. By distinguishing between knowledge by acquaintance (direct awareness of sense data) and knowledge by description, Russell sought to logically reconstruct our understanding of the external world from the foundation of immediate experience.32

Ludwig Wittgenstein

While Wittgenstein was deeply involved in the development of logical atomism, his focus in the Tractatus Logico-Philosophicus differed from Russell’s constructionist project. Wittgenstein emphasized that the logical structure of language mirrors the structure of empirical reality, where "atomic propositions" correspond to "atomic facts". Unlike Russell, who used sense data as a foundational building block for physical objects, Wittgenstein’s "picture theory of meaning" focused on how language represents states of affairs, asserting that the logical form of reality is "shown" through the structure of language rather than described by it.14