 In response to this discussion, Ian Jarvie (1966) proposed as important questions for a philosophy of technology what the epistemological status of technological statements is and how technological statements are to be demarcated from scientific statements. This suggests a thorough investigation of the various forms of knowledge occurring in either practice, in particular, since scientific knowledge has already been so extensively studied, of the forms of knowledge that are characteristic of technology and are lacking, or of much less prominence, in science. A distinction between ‘knowing that’—traditional propositional knowledge—and ‘knowing how’—non-articulated and even impossible-to-articulate knowledge—had been introduced by Gilbert Ryle (1949) in a different context. The notion of ‘knowing how’ was taken up by Michael Polanyi under the name of tacit knowledge and made a central characteristic of technology (Polanyi 1958); the current state of the philosophical discussion is presented in this encyclopedia’s entry on  knowledge how.  However, emphasizing too much the role of unarticulated knowledge, of ‘rules of thumb’ as they are often called, easily underplays the importance of rational methods in technology. An emphasis on tacit knowledge may also be ill-fit for distinguishing the practices of science and technology because the role of tacit knowledge in science may well be more important than current philosophy of science acknowledges, for example in concluding causal relationships on the basis of empirical evidence. This was also an important theme in the writings of Thomas Kuhn on theory change in science (Kuhn 1962).