This paper examines the position of negative adverbs such as mie, pas, point and jamais in Middle and Classical French infinitival clauses. Instead of linking the movement of the infinitival verb to the strength of functional categories such as AGRℴ, I propose to link it to a parametric change of NEGP from strong to weak. Up to Classical French, the infinitival verb can move to AGRℴ because NEGP is strong; this movement of the infinitival verb to AGRℴ allows the movement of negative adverbs, which are base-generated in VP initial position. At the beginning of Classical French, a parametric change affected the strength of NEGP, from strong to weak. As a result of this parametric change, movement of the infinitival verb to AGRℴ becomes more limited. Moreover, the difference between pas and other negative adverbs is due to a change in the nature of pas, from an adverb base-generated in VP initial position which can move, to a fixed adverb base-generated in the specifier position of NEGP.