 The Intuition/Deduction thesis claims that we can know some propositions by intuition and still more by deduction. Since traditionally this thesis was thought to be rejected by empiricists and adopted only by rationalists, it is useful to become more familiar with it. In a very narrow sense, only rationalists seem to adopt it. However, the current consensus is that most empiricists (e.g., Locke, Hume, Reid) have been willing to accept a version of the thesis, namely inasmuch as it is restricted to propositions solely about the relations among our own concepts. We can, they agree, know by intuition that our concept of God includes our concept of omniscience. Just by examining the concepts, we can intellectually grasp that the one includes the other. The debate between rationalists and empiricists is joined when the former assert, and the latter deny, the Intuition/Deduction thesis with regard to propositions that contain substantive information about the external world. Rationalists, such as Descartes, have claimed that we can know by intuition and deduction that God exists and created the world, that our mind and body are distinct substances, and that the angles of a triangle equal two right angles, where all of these claims are truths about an external reality independent of our thought. Such substantive versions of the Intuition/Deduction thesis are our concern in this section.