 The formal logical sentence with this meaning is known as the Barcan Formula, after Ruth C. Barcan, who published the first systematic treatment of quantified modal logic, in which she postulated the formula as an axiom (Barcan 1946), and who has published under the name ‘Ruth Barcan Marcus’ since 1950. If we read ‘F’ as meaning “non-identical with every actual object”, the Barcan Formula says that if it is possible that something is non-identical with every actual object, then something x is such that it is possible that x is non-identical with every actual object. The antecedent is plausibly true, for there could have been more objects than the actual ones. But if so, the consequent is true as well, assuming the truth of the Barcan Formula. But no actual object is non-identical with every actual object, for every actual object is identical with itself, an actual object. Assuming the necessity of identity, if an object y is identical with an object z, it is not possible that y is non-identical with z. So, no actual object is such that it is possible that it is non-identical with every actual object. Therefore, any object x such that it is possible that x is non-identical with every actual object must be a non-actual possible object.