 These different notions of simplicity are not only conceptually distinct, they are often mutually incompatible or conflicting. Nowhere has this become more evident than in the chimpanzee theory of mind debate. The last few years have witnessed a huge controversy over the experimental results in this research area. A number of studies have shown that chimpanzees can use information regarding what a competitor has visual access to in order to decide whether or not to go for a reward (Hare et al. 2000; Hare, Call, &amp; Tomasello 2001; Karg et al. 2015; Melis, Call, &amp; Tomasello 2006). The controversy arose because these experimental results can in principle be explained by positing that chimpanzees were reasoning about the mental states of others (in this case, about what they could or could not see), or that they were solely reasoning about their behavior (e.g., about their bodily orientation or the existence of an uninterrupted line of gaze between their eyes and the reward). What is interesting about this controversy is that the defenders of each of these options were both claiming to be offering the simplest explanation of the data. For Michael Tomasello and Josep Call (2006), it’s more parsimonious to assume that chimpanzees can understand what others can and cannot see rather than posit that they have learned a different behavioral rule for every relevant situation that involves a competitor’s line of gaze. For Povinelli and Jennifer Vonk (2004), mental state attributions can only be inferred from another’s behavior, which means that every mindreader must also be a behavior reader. Since the opposite is not the case, it’s more parsimonious to assume that chimpanzees are behavior readers rather than mindreaders. The chimpanzee theory of mind controversy perfectly illustrates that the issue of simplicity is a philosophical one, meaning that the question of whether, to what extent, and in what sense simpler explanations ought to be preferred is one that cannot be settled solely through empirical measurements or mathematical calculations, but requires philosophical analysis and argumentation (for discussions, see Clatterbuck 2017, 2018; Sober 2015).