 Libertarians, while united in endorsing this negative condition on sourcehood, are deeply divided concerning which further positive conditions may be required. It is important to note that while libertarians are united in insisting that compatibilist accounts of sourcehood are insufficient, they are not committed to thinking that the conditions of freedom spelled out in terms either of reasons-responsiveness or of identification are not necessary. For example, Stump (1988, 1996, 2010) builds a sophisticated libertarian model of free will out of resources originally developed within Frankfurt’s identification model (see also Ekstrom 1993, 2000; Franklin 2014) and nearly all libertarians agree that exercises of free will require agents to be reasons-responsive (e.g., Kane 1996; Clarke 2003, chs. 8–9; Franklin 2018, ch. 2). Moreover, while this section focuses on libertarian accounts of sourcehood, we remind readers that most (if not all) libertarians think that the freedom to do otherwise is also necessary for free will and moral responsibility.