In Weaving the Web (2000), Berners-Lee defines Social Machines as biotechnologically hybrid Web-processes on the basis of which, "high-level activities, which have occurred just within one human's brain, will occur among even larger more interconnected groups of people acting as if the shared a larger intuitive brain" (201-202). The analysis and design of Social Machines has already started attracting considerable attention both within the industry and academia. Web science, however, is still missing a clear definition of what a Social Machine is, which has in turn resulted in several calls for a "philosophical engineering" (Halpin 2013; Hendler & Berners-Lee, 2010; Halpin et al., 2010). This paper is a first attempt to respond to this call, by combining contemporary philosophy of mind and cognitive science with epistemology. The idea of philosophical engineering implies that a sufficiently good conception of Social Machines should be of both theoretical and practical advantage. To demonstrate how the present approach can satisfy both objectives it will be used in order to address one of Wikipedia's (the most famous Social Machine to date) most worrying concerns-i.e., the current and ongoing decline in the number of its active contributors (Halfacker et al., 2012).