  (b) Anything purely physical operates solely according to physical laws operating on its physical properties: it does not, at bottom, operate according to meanings, senses, or propositional content. As a ‘thinking machine’, it is what Dennett (1987: 61) calls ‘a syntactic engine’, where ‘syntax’ is used, somewhat extendedly, to signify merely the physical structure of symbols and the consequent rules of their operation, rather than their meaning. The issue is whether, under this constraint, one can give an account for meaningful communication and understanding at all.