Head movement is subject to the Head Movement Constraint, according to which when a head moves, it cannot skip an intervening head. Left adjunction and the Head Movement Constraint ensure that the Mirror Principle holds. The syntactic mechanism responsible for the effects of the Mirror Principle is head movement: heads raise and left-adjoin to higher heads. The general principle behind morpheme order is the Mirror Principle (first formulated by Baker 1985), according to which the linear order of morphemes is the mirror image of the hierarchy of syntactic projections. For example, in a plural noun like "cat-s", the plural morpheme is higher in the hierarchy than the noun: [NumP -s[NP cat]]. The Mirror Principle dictates that the linear order of the plural morpheme with respect to the noun should be the mirror image of their hierarchy, namely the attested "cat-s".