In his 1978 article “Language, epistemology, and mysticism”, Steven T. Katz presents his theory of the interpretation of mystical experience reports in which the foundational epistemological claim is that “there are no pure experiences”. Around this claim, a theory of interpretation is developed that implies the rejection of a common core in mystical experience. This also involves a criticism against the so called perennial interpretations of mystical experience and of the phenomenal characteristics that are considered to be prevalent in mystical experiences across traditional religious boundaries. Katz’s theory has been interpreted and criticised as a ‘constructivist’ theory of meaning, implying cognitive relativism and non-realism for the experiences of mystics, though in the light of Katz’s own claims, his theory should be understood as a ‘contextualist’ theory which allows for reality to impact on the individual mystics experience. As a theory of interpretation, purporting to be superior to the perennial models of interpretation, Katz’s theory is evaluated in terms of ‘scientific value’ for the interpretation of mystical reports. The criteria for this evaluation are: (a) the theory’s ability to establish precise demarcation standards for mystical experiences, (b) the theoretical consistency displayed by the theory, (c) the extent to which the theory shows regard for the validity of the selfunderstanding of the mystics, and (d) the theory’s potential to advance the current understandings of the field. The analysis is based on three problem areas in Katz’s theory: (1) the rejection of the common phenomenal characteristics of mystical experience in favour of the ‘object’ that the mystics experience, (2) Katz’s view on the problematic relation between facilitative techniques and the experiences of mystics which involves the idea that mystical experience is overdetermined by pre-experiential beliefs and expectations, and (3) Katz’s view that mystical experience is conserving religious doctrine and that the ‘models’ of each major religious tradition inform coming generations of mystics what to experience. If the criticisms presented in this thesis are correct and Katz theory fails to satisfy the first three criteria (a) – (c), then it seems to follow that an advancement of the understanding of the field cannot come into question.