Some of the methods for data collection in experimental psychology, as well as many of the inferences from observed behavior or image scanning, are based on the implicit premise that language use can be linked, via the meaning of words, to specific subjective states. Wittgenstein’s well known private language argument (PLA), however, calls into question the legitimacy of such inferences. According to a strong interpretation of PLA, all of the elements of a language must be publicly available. Thus the meaning (...) of words is not fixed by reference to our private experiences, and so data from subjective state claims indicates nothing about our subjective experiences. Application of PLA to psychological studies based on descriptions of the experience of orgasm offers support for the strong version of the conclusion of PLA. We show that PLA has deep implications for data collection methods and inferences in experimental psychology. In particular we critique two contemporary research projects in neuroscience: one studying the ability to remember emotionally loaded words and the other studying experience of attraction. Both of these projects attempt to link subjective experiences and thought processes to particular observable brain states. The research methods appeal to (implicit) inferences from linguistic usage to subjective states. Application of PLA will show that such inferences cannot be made because the meaning of a word is not determined by any subjective state of the speaker. (shrink)