Heidegger introduces the notion of Mitsein to combat a philosophical picture – specifically, a Cartesian picture – in which the individual mind, groping to pin down with apodictic certainty the existence of something outside itself, must bridge some sort of metaphysical gap between itself and other people. That is to say, Heidegger wants to help us escape from a philosophical paradigm that would have us forget that, phenomenologically, my world is not anchored in some solipsistic vanishing point, bounded at its limits by a transcendental “I,” but rather “is always the one that I share with Others” (see §26 of Being and Time). My view is that it is this simple, yet fateful, ontological claim of Heidegger’s that Beauvoir appropriates. Beauvoir appeals to the concept of Mitsein in The Second Sex not to endorse or deny the idea that human beings are bonded to one another in some sort of fellowship or community but to acknowledge, along with Heidegger, that his way of sidestepping the so-called “problem of other minds” raises a new problem: the problem of how an individual is to find the courage to be herself, to distinguish herself, to find her voice, in a world in which she is inevitably with – even smothered by – others, and particularly, by men. I read Beauvoir as appropriating the concept of Mitsein in The Second Sex in her quest to understand why men and women are inclined to exploit the fact of sex difference as a way of negotiating their fundamental fear of being human – of being, that is to say, endlessly tempted to let themselves be reified (for men as essentially “for-itself” and for women as essentially “in-itself”) in the objectifying judgments of others.