Abstract: In the early 18th century, the metaphysics of time was hotly contested. The controversy between Leibniz and Clarke (on Newton's behalf) is well known, but less attention has been given to Émilie Du Châtelet. In her Institutions de physique, she presents a theory of time which seems to synthesize these two conflicting accounts. Her theory retains the predictive empirical aspects of Newton's Absolutism while cohering with the metaphysical principles of Leibniz. In short, Du Châtelet contends that while the Newtonian ontological independence of time would violate the principle of sufficient reason (as Leibniz argued) and her rules of "good hypothesis making", she retains Newton's time as an ideal being and agrees with him that it empirically appears to be an independently-subsisting being composed of continuous, successive parts which flow uniformly. Du Châtelet grounds the possibility of this ideal being by an innovative subjective and psychological account, predating the epistemological-shift of Immanuel Kant and psychological-shift of William James. I argue that she accomplishes this by means of two distinct, abstractive processes of the mind, i.e., what I term, the "gathering-activity" and the "comparing-activity". I demonstrate that while the gathering-activity is the condition for the possibility for an entity to be in time, the comparing-activity is the condition for the possibility of an entity to exist through time. Thus, I argue, for Du Chatelet, time is radically subjective. I further highlight this claim by juxtaposing her own writing with that of William James, who makes similar claims regarding the subjective nature of time and its measurement.