 This account relies on several unexplained notions, such as square (of tape), symbol, scanning, and carrying out an instruction. Furthermore, the account is specified in terms of TM tables, but there are other kinds of computational description. A general account of concrete computation should cover other computational descriptions besides TM tables. Perhaps for these reasons, Putnam—soon followed by many others—abandoned reference to squares, symbols, etc.; he substituted them with an appeal to a physical description of the system. The result of that substitution is what Godfrey-Smith (2009) dubs the “simple mapping account” of computation.