 One of the perennial topics in philosophy of science concerns inter-theoretic relations. In the course of debating whether biology is reducible to the physical sciences or whether psychology is reducible to biology, many philosophers assume that chemistry has already been reduced to physics. In the past, this assumption was so pervasive that it was common to read about “physico/chemical” laws and explanations, as if the reduction of chemistry to physics was complete. Although most philosophers of chemistry would accept that there is no conflict between the sciences of chemistry and physics (Needham 2010b), many would reject a stronger unity thesis. Most believe that chemistry has not been reduced to physics nor is it likely to be (see Le Poidevin 2005, for the opposite view, and Hendry &amp; Needham 2007, for a rejoinder).