This argument has elicited numerous replies and counter-replies. Some argue that neural networks can exhibit systematicity without implementing anything like classical computational architecture (Horgan and Tienson 1996; Chalmers 1990; Smolensky 1991; van Gelder 1990). Some argue that Fodor and Pylyshyn vastly exaggerate systematicity (Johnson 2004) or productivity (Rumelhart and McClelland 1986), especially for non-human animals (Dennett 1991).  These issues, and many others raised by Fodor and Pylyshyn’s argument, have been thoroughly investigated in the literature.  For further discussion, see Bechtel and Abrahamsen (2002: 156–199), Bermúdez (2005: 244–278), Chalmers (1993), Clark (2014: 84–86), and the encyclopedia entries on  the language of thought hypothesis  and on   connectionism.