 As to be expected, there is some controversy regarding the interpretation of these tenets; for instance, tenet 2 is sometimes extended to also include non-initial states (see Whipple, 206). There is another important aspect of the pre-established harmony. A substance’s expressions arising “from the depths of its own nature” are also called perceptions by Leibniz. Perception is “[t]he passing state which involves and represents a multitude in a unity” (Monadology §14 GP vi, 608/AG 214). The pre-established harmony consists in the isomorphic mapping of perceptions and bodily motions. Whenever a substance has a perception x there will be a corresponding bodily state y expressing that perception x. So when I perceive myself as putting a log in the fire “[my] animal spirits and [my] blood [take] on, at exactly the right moment, the motions required to correspond to the passions and the perceptions of [my] soul” (New System GP iv, 484/L 458).