Martin Buber best known for his philosophy of dialogue, a form of existentialism centered on the distinction between the I–Thou relationship and the I–It relationship. In "I and Thou", Buber introduced his thesis on human existence; Ich‑Du is a relationship that stresses the mutual, holistic existence of two beings. It is a concrete encounter, because these beings meet one another in their authentic existence, without any qualification or objectification of one another. Even imagination and ideas do not play a role in this relation. In an I–Thou encounter, infinity and universality are made actual (rather than being merely concepts). The "Ich-Es" ("I‑It") relationship is nearly the opposite of "Ich‑Du". Whereas in "Ich‑Du" the two beings encounter one another, in an "Ich‑Es" relationship the beings do not actually meet. Instead, the "I" confronts and qualifies an idea, or conceptualization, of the being in its presence and treats that being as an object. All such objects are considered merely mental representations, created and sustained by the individual mind.