 The argument seems straightforward so long as we read “Father” and “Son” as merely singular referring terms. But Leftow asserts that they are also definite descriptions “which may be temporally rigid or non-rigid” (Leftow 2012b, 334–5). A temporally rigid term refers to a being at all parts of its temporal career. Thus, if “the president of the United States” is temporally rigid, then in the year 2013 we may truly say that “The president of the United States lived in Indonesia”, not of course, while he was president, but it is true of the man who was president in 2013, that in his past, he lived in Indonesia. If the description “president of the United States” (used in 2013) is not temporally rigid, then it refers to Barack Obama only in the presidential phase of his life, and so the sentence above would be false.