 Let us now return to the primary question of this section: how should we understand the distinction between knowledge by acquaintance and knowledge by description? When philosophers speak of knowledge they typically mean to be discussing knowledge of truths or propositional knowledge, knowledge that involves a belief or judgment in some true claim or proposition. As introduced by Russell, the distinction sometimes seems to be that between noninferential or foundational knowledge on the one hand, and inferential or nonfoundational knowledge on the other. Roughly, one has nonfoundational or inferential knowledge that p when one’s knowledge that p depends on one’s knowledge of some other proposition(s) from which one can legitimately infer p; and one has foundational or noninfrential knowledge that p when one’s knowledge that p does not depend on any other knowledge one has. Knowledge by acquaintance is foundational knowledge because it depends on one’s acquaintance with the object itself, or with properties of or facts about the object, and not on any further knowledge of truths. Knowledge by description, in contrast, always depends on some further knowledge of truths for support; as Russell puts it, knowledge by description “always involves…some knowledge of truths as its source and ground” (1912: 72–3, emphasis added).