 Frequently discussed is the skeptical challenge raised by Kathleen Wilkes. She expresses a deep suspicion of scenarios such as Derek Parfit’s people splitting like an amoeba (see Parfit 1987; Gendler 2002a). Wilkes wants philosophy “to use science fact rather than science fiction or fantasy” (Wilkes 1988, p. 1), and therefore to refrain from using thought experiments because they are “both problematic and positively misleading” (Wilkes 1988, p. 2). She claims that thought experiments about personal identity in particular often fail to provide the background conditions against which the experiment is set (see Wilkes 1988, p. 7). She thinks we would not know what to say if we encountered someone who split like an amoeba. She insists that a legitimate thought experiment must not violate the known laws of nature. We do agree with Wilkes that underdetermination can be a problem. But instead of dismissing thought experiments in philosophy we should consider it a crucial factor in assessing the quality of a thought experiment (see Rescher 2005, pp. 9–14). The more detailed the imaginary scenario in the relevant aspects, the better the thought experiment (see Brendel 2004, pp. 97–99; Häggqvist 1996, p. 28).