 Different accounts of theory reduction and explanatory reduction face several potential problems. Some critiques of (epistemic) reductionism emphasize that the effects of molecular processes strongly depend on the context in which they occur, so that one molecular kind can correspond to many higher level kinds  (Section 4.1).  Another significant challenge to reductionism stems from the fact that higher level biological structures and processes can be (and typically are) realized by different kinds of molecular processes, so that many molecular kinds can correspond to one higher level kind  (Section 4.2).  Finally, because biological processes must be represented before they can be explained (Sarkar 1998), two further features become salient as issues for explanatory reduction: temporality and intrinsicality  (Section 4.3).