This work investigates the philosophical problem of how human perception confirms the existence of an external, objective universe independent of the mind. Mary Shepherd, a prominent 19th-century Scottish philosopher, utilizes a rigorous analytical framework to challenge the skeptical conclusions of David Hume and George Berkeley. She argues for a causal theory of perception, asserting that our sensory experiences provide reliable evidence of external objects through the principle of cause and effect.

Scholars frequently highlight this text as a significant contribution to early 19th-century British philosophy, particularly for its sophisticated defense of realism. Experts note that Shepherd's prose is dense and requires careful attention to her specific logical definitions.