This paper seeks to examine two moments of the subject’s identification with substance in modernity, namely, the body in Hobbesian philosophy and the individual substance in Leibnizian thought. In Hobbes, to be a subject signifies to be subjected (to imaginary space, to the movements transmitted by means of shock, as well as to the sovereign), so that the body-substance is characterized by not having in itself its principle of movement. In Leibniz, for his turn, a subject (understood as substance) is that which contains in its own nature everything that can be truly predicated about it, implying that it is the foundation and principle of its own activity, or, in a word, it is self-sufficient. Nonetheless, although Hobbesian body is characterized by its inertia and Leibnizian substance by its self-sufficiency, it is my purpose to indicate that the former is more crucial than the latter to the constitution of the modern conception of subjectivity, i.e., of the subject as the center of action and as a founding power, capable of establishing a new order by its decision. This is not possible in Leibnizian philosophy, for, according to it, human activity, like that of any other substance, consists solely in the actualization of the divine plan of the best of all possible worlds.