   Soon after Principia Mathematica, Russell became convinced that this picture was too simplistic. In the “Philosophy of Logical Atomism” lectures he described a more complicated framework. In the new terminology, the phrase “atomic fact” was introduced for the simplest kind of fact, i.e., one in which n particulars enter into an n-adic relation.  He used the phrase “atomic proposition” for a proposition consisting only of a predicate for an n-place relation, along with n proper names for particulars. Hence, such propositions could take such forms as “F(a)”, “R(a, b)”, “S(a, b, c)” (cf. PM2, xv).  An atomic proposition is true when it corresponds to a positive atomic fact. However, Russell no longer conceived of falsity as simply lacking a corresponding fact. Russell now believed that some facts are negative, i.e., that if “R(a, b)” is false, there is such a fact as a’s not bearing relation R to b. Since the proposition “R(a, b)” is affirmative, and the corresponding fact is negative, “R(a, b)” is false, and, equivalently, its negation “not-R(a, b)” is true. Russell’s rationale for endorsing negative facts was somewhat complicated (see, e.g., PLA, 211–15); however, one might object that his earlier view, according to which “R(a, b)” is false because it lacks a corresponding complex, is only plausible if you suppose that it must be a fact that there is not such a complex, and such a fact would itself seem to be a negative fact.