Another problem for machine functionalism, also highlighted by Block and Fodor (1972), concerns the systematicity of thought. An ability to entertain one proposition is correlated with an ability to think other propositions. For example, someone who can entertain the thought that John loves Mary can also entertain the thought that Mary loves John. Thus, there seem to be systematic relations between mental states. A good theory should reflect those systematic relations. Yet machine functionalism identifies mental states with unstructured machines states, which lack the requisite systematic relations to another. For that reason, machine functionalism does not explain systematicity. In response to this objection, machine functionalists might deny that they are obligated to explain systematicity. Nevertheless, the objection suggests that machine functionalism neglects essential features of human mentality. A better theory would explain those features in a principled way.