This paper demonstrates how Mary Astell's version of Cartesian dualism supports her disavowal of female subordination and traditional gender roles, her rejection of Locke's notion of "thinking matter" as a major premise for rejecting his political philosophy of "social contracts" between men and women, and, finally, her claim that there is no intrinsic difference between genders in terms of ratiocination, the primary assertion that grants her the title of the first female English feminist.