 Loar emphasizes versions of (2) and (3) over (1) and (4), but one sees conditions of this sort at least briefly alluded to by a number of functionalist philosophers, including Dennett (1969, 1978), Armstrong (1973), Stalnaker (1984), Fodor (1990), Pettit (1993), Shoemaker (2003), and Zimmerman (2018). For the functionalist, to believe just is to be in a state that plays (something like) this sort of causal role.