This paper evaluates karl popper's claim in his "conjectures and refutations" that berkeley's "nominalism" is at the root of his "instrumentalist" philosophy of science. the argument of the paper is divided into two parts. in the first part, it is argued that, according to berkeley, "thought" is ontologically prior to "language". in this sense, berkeley's instrumentalism is rooted in a metaphysics of experience and not in a theory of language. in the second part, it is argued that the meaning of (...) 'meaning', according to berkeley, is not governed, as popper suggests, by purely empirical criteria. it is shown that berkeley actually employs several criteria of meaning, only one of which involves the association of a word with a corresponding sense experience. (shrink)