  One could legitimately ask for more, in particular for some account that made intelligible why those links hold and perhaps why they could not fail to do so. A familiar two-stage model for explaining macro-properties in terms of micro-substrates is often invoked. In the first step, one analyzes the macro-property in terms of functional conditions, and then in the second stage one shows that the micro-structures obeying the laws of their own level nomically suffice to guarantee the satisfaction of the relevant functional conditions (Armstrong 1968, Lewis 1972).