 Free logic is formal logic whose quantifiers are interpreted in the usual way—that is, objectually over a specified domain \(\bD\)—but whose singular terms may denote objects outside of \(\bD\), or not denote at all. Singular terms include proper names (individual constants),  definite descriptions,  and such functional expressions as ‘\(2 + 2\)’. Since  classical (i.e., Fregean) predicate logic  requires that singular terms denote members of \(\bD\), free logic is a “nonclassical” logic. Where \(\bD\) is, as usual, taken to be the class of existing things, free logic may be characterized as logic the referents of whose singular terms need not exist.