Can Economics can be a separate Science?

Mill (1872, 1874) is an early proponent of the thesis that economics has a special domain in which it can operate relatively independently of findings from other sciences. Contra Mill, I argue that this so-called separateness-thesis is best defendedunder an externalist interpretation of Rational Choice Theory (RCT). Mill’s defence is consistent with an internalist interpretation of RCT. Internalism holds that RCT depicts psychological mechanisms operating in economic agents. I argue that such a defence fails to establish separateness, because it makes economics highly depended on psychological findings. However, externalism understands RCT as an adequate description of how agents react to incentives if certain environmental structures are present. Under this interpretation, we can defend separateness by investigating which features of an environmental structure will lead agents to behave in accordance with RCT. Thereby, we can derive indicators that enable us to demarcate a separate domain for economics.