 (K1)—one  of the so-called “Kripke conditionals”—is a modal premise that instantiates “If \(p\), then necessarily \(p\)”, which he suggests is something we know “by a priori philosophical analysis” (1971: 180; 1980: 108). On the other hand,  (K2)  is a non-modal, factual premise that we may come to know empirically. It was an empirical discovery that the celestial body that we call “Hesperus” for its evening sightings was the same one as the one we call “Phosphorus” for its morning sightings, namely the planet Venus. As a consequence of the empirical contribution of (K2), the conclusion of the argument,  (K3),  is also a posteriori. (For further discussion, see Casullo 1977, 2010; Peacocke 1999). Note that not all instances of “If \(p\), then necessarily \(p\)” will be true. In this paradigm case, \(p\) is an identity statement involving rigid designators on both sides. These statements are such that if true, they are necessarily true, which is something most philosophers hold we can know a priori. (See also the entry on  rigid designation).