 Popper was initially uneasy with the concept of truth, and in his earliest writings he avoided asserting that a theory which is corroborated is true—for clearly if every theory is an open-ended hypothesis, then ipso facto it has to be at least potentially false. However, he came to accept Tarski’s reformulation of the correspondence theory of truth, and in Conjectures and Refutations (1963) he integrates the concepts of truth and content to frame the metalogical concept of “truthlikeness” or “verisimilitude”. A “good” scientific theory, Popper argues in that work, has a higher level of verisimilitude than its rivals, and he explicates this concept by reference to the logical consequences of theories. A theory’s content is the totality of its logical consequences, which can be divided into two classes: