Given the key assumption of Trace Theory that a moved constituent leaves behind a coindexed trace, we might formulate the relevant principle that transformations cannot downgrade constituents in terms of an equivalent condition that a moved constituent cannot occupy a lower position than any of its traces. This principle might be stated more formally as in (85) below

(85) C-COMMAND CONDITION

(85) A moved constituent must c-command ( = constituent-command)

(85) each of its traces at S-structure (X c-commands Y just in case the

(85) first branching node dominating X dominates Y, and neither X

(85) nor Y dominates the other)