ABSTRACT. The demand for 'criteria of correctness' to identify recurring particulars in Wittgenstein's private language argument favors an idealist interpretation of quantum phenomena. The indeterminacy principle in quantum physics and the logic of the private language argument share a common concern with the limitations by which microphysical or sensation particulars can be reidentified. Wittgenstein's criteria for reidentifying particular recurrent private sensations are so general as to apply with equal force to quantum particulars, and to support the idealist thesis that quantum phenomena are themselves essentially mental or dependent on mental occurrences.