obiectum quo (Latin ‘object by which’), in medieval and Scholastic epistemology, the object by which an object is known. It should be understood in contrast with obiectum quod, which refers to the object that is known. For example, when a person knows what an apple is, the apple is the obiectum quod and his concept of the apple is the obiectum quo. That is, the concept is instrumental to knowing the apple, but is not itself what is known. Human beings need concepts in order to have knowledge, because their knowledge is receptive, in contrast with God’s which is productive. (God creates what he knows.) Human knowledge is mediated; divine knowledge is immediate. Scholastic philosophers believe that the distinction between obiectum quod and obiectum quo exposes the crucial mistake of idealism. According to idealists, the object of knowledge, i.e., what a person knows, is an idea. In contrast, the Scholastics maintain that idealists conflate the object of knowledge with the means by which human knowledge is made possible. Humans must be connected to the object of knowledge by something (obiectum quo), but what connects them is not that to which they are connected. A.P.M.