NANS, my explanation is that solid describes the aggregate state, and that firm is just an attribute within the solid state, basically a generalization of a mix

NANS, my explanation is that solid describes the aggregate state, and that firm is just an attribute within the solid state, basically a generalization of a mixture of sub-attributes (density/distance and cohesion) Tight refers to density, strong to cohesion. So something within that range that's very dense and cohesive is hard, and something that isn't is soft.