   Although Russell did not use the phrase “logical atomism” in the Introduction to Principia Mathematica, in many ways it represents the first work of Russell’s atomist period. Russell there explicitly endorsed the view that the “universe consists of objects having various qualities and standing in various relations” (PM, 43).  Propositions that assert that an object has a quality, or that multiple objects stand in a certain relation, were given a privileged place in the theory, and explanation was given as to how more complicated truths, including truths about classes, depend on the truth of such simple propositions. Russell’s work over the next two decades consisted largely in refining and expanding upon this picture of the world.