The theory of “knowledge by presence” has a special place in the Sadra system. “Knowledge by presence” is both a theory of knowledge in Sadra's philosophy and a theory for explaining self-knowledge. Reflecting on this important theory will immediately make us realize its complex and mysterious nature. The present paper intends to provide an accurate and clear reading of this theory in a clearer language in the form of a comparative approach between this theory and one of the most important theories of self-knowledge in the analytic philosophy, namely the theory of “Knowledge by acquaintance”. At first glance, Russell's theory of “Knowledge by acquaintance” is one of the most similar to Sadra's theory. Such characteristics as the condition of presence, immediacy, and infallibility are examples of the similarity of these two theories. But the discussion of “unity of the knower and the known” in Sadra's theory is the point of separation between the two theories, and in fact, it is a place that will seriously challenge the claim of closeness between these theories. Finally, perhaps with some tolerance, Russell's theory is a primitive and incomplete picture of Sadra's theory. Furthermore, it should be noted that understanding these two theories in the context of the different philosophical systems of these two philosophers -namely Sadra's theory of Unity and originality of existence and Russel's theory of Knowledge by Acquaintance- makes it more difficult to claim the deep closeness between these two theories.