  At the end of the section on topic neutrality, we distinguished two notions of topic neutrality. The first notion—insensitivity to the distinguishing features of individuals—is effectively captured by the permutation invariance criterion. How might we capture the second—universal applicability to all thought or reasoning, regardless of its subject matter? We might start by identifying certain ingredients that must be present in anything that is to count as thought or reasoning, then class as logical any expression that can be understood in terms of these ingredients alone. That would ensure a special connection between the logical constants and thought or reasoning as such, a connection that would explain logic’s universal applicability.