This is the first of two assignments in which Kripke turns from proper names to terms for substances or “natural kinds.” As his opening comments suggest, he will eventually focus on a sort of identity statements involving such terms, but he first addresses their meaning.
• Kripke introduces the issue briefly in the first pargraph of this assignment (pp. 115f).
• Next (pp. 116-123) he discusses the meaning of natural kind terms in a way that is analogous to his discussion of the meaning of proper names. He states the analogy explicitly in a later paragraph (pp. 127f).
• In between (pp. 123-127) is a discussion analogous to his discussion of the essential properties of particular objects. Indeed, the statements he considers in here will often amount to generalizations whose instances ascribe essential properties to individuals.
• In the final part of this assigment (pp. 128-134) Kripke finally addresses identities between natural kind terms. Pay particular attention to his discussion of heat since that example will play a role also in the final part of lecture III.