Advocates of the former, the Normative Principle, argue that attributions of intentional idioms to physical systems should be the propositional attitudes that the physical system ought to have in those circumstances (Dennett 1987, 342). However, exponents of this view are still further divided into those who make an "Assumption of Rationality" and those who adhere to the "Principle of Charity". Dennett (1969, 1971, 1975), Cherniak (1981, 1986), and the more recent work of Putnam (1983) recommend the Assumption of Rationality, which unsurprisingly assumes that the physical system in question is rational. Donald Davidson (1967, 1973, 1974, 1985) and Lewis (1974) defend the Principle of Charity.