Characteristic of model based science is its attachment to idealizations and abstractions. Idealizations are expressed by statements known to be false. Abstractions are suppressors of what is known to be true. Idealizations over-represent empirical phenomena. Abstractions under-represent them. In a sense, idealization and abstractions are one another's duals. Either way, they are purposeful distortions of phenomena on the ground. Sometimes phenomena on the ground approximate to what their idealizations say of them. Sometimes nothing in nature approaches them in any finite degree. So wide is this gulf between reality and idealization that Nancy Cartwright was moved to say of them that they are "pure fictions".