[Loneliness] comes from a vague core of the self’ wrote Sylvia Plath. I think Plath is right. To show why, I turn to Kant. For Kant, what lies at the ‘core of the self’ is our capacity for self-consciousness. But, self-consciousness, Kant warns, opens an ‘abyss’ between the active ‘I’ of which we are conscious and the passive phenomenal world we experience. Loneliness, I here argue, is the painful experience of standing on the ‘brink of the abyss’, from the standpoint of the noumenal ‘I’. Like Kant, but unlike Plath, I think there is a way out of the ‘prison of the self’ – as Kant calls it. To escape the prison, we need a fellow agent to come to this side of the abyss - a fellow agent with whom we can ‘unite our will’ in shared action and thought. We escape the loneliness of the self-conscious ‘I’ in a shared ‘we’. This is why friends offer an escape from the prison. With our friends, Kant says, we form a ‘single moral person’. Yet, it is also why, as empirical findings show, being part of a sports team or a choir, having a conversation with someone we love or a stranger on the train are all ways in which we can tear down the walls of the prison of the self.