  Although Leibniz recognizes “firmness” as an important  passive power attributable to bodies, like many other mechanists, he  is reluctant to posit the existence of primitive attractive forces  in nature (SD II.52/AG 136; see also Leibniz’s Fifth Letter to  Clarke, paragraph 35/Alexander 66). He thus insists that firmness is  a derived passive power of bodies since “we should not explain  firmness except through the surrounding bodies pushing a body  together” (SD II.52/AG 136). 