Rigidez, esencialismo y actualismo en los términos referenciales para clases naturales

saul kripke (1980, 2005), in his third lecture, extends his notion of rigid designator to referential terms for natural kinds. this raises the question whether his semantic theory is neutral in questions of metaphysics and, especially, if his account of identity statements for natural kinds implies some form of "non trivial" essentialism. one option is closed: it is not plausible to understand that the truth values for sentences involving these terms are determined by reference instances of a natural kind k, so the question is: is the kripkean semantic conception for natural kinds nominalist? on the other hand, considering the kripkean statement that a possible world is understandable from the notion of "counterfactual situation", a closely related question is whether kripke shares an actualist position and, consequently, whether he rejects the idea that in the possible worlds where there is no natural kind k, this should be understood as consisting of mere possibilia. this is because it does seem plausible to assert the necessary existence as an essential property of a natural kind. this paper discusses the links between these three notions: actualism, essentialism and rigidity. i take into account mainly the ideas of n. salmon, s. soames, o. simchen and d. ackerman, among others. finally there is a response to the above questions, which focuses on maintaining one of the central theses of kripke's semantic theory, namely that identity statements involving rigid referential terms are necessarily true, if true.