The extent to which a hypothesis approaches the truth. The first attempt to define this notion, due to Popper, identifies this with the extent to which a theory captures the whole truth: a theory T will have more verisimilitude than a rival T’ just in case T implies more truths and fewer falsities than T’. But the formal development of the notion has proved extremely tricky, especially as the verisimilitude of theories is apt to vary with variations in the language in which they are couched.