 There are some differences between Sider’s approach and this higher-order approach. One is that Sider does not think of ‘Structural’ as ambiguous, despite its ability to occupy different syntactic roles. One upshot is that for him there is just a single question ‘Structural(Structural)?’ where a higher-order approach would distinguish infinitely many: ‘Structural\(_{\langle\langle e\rangle\rangle}\)(Structural\(_{\langle e\rangle})\)?’, ‘Structural\(_{\langle\langle\langle e\rangle\rangle\rangle}\)(Structural\(_{\langle\langle e\rangle\rangle})\)?’, and so on. Another is that Sider allows ‘Structural’ to combine with linguistic items that would not, on the higher-order approach, be meaningful units at all, such as  variable-binders.[7]  Indeed Sider suggests that we can make sense of attributions of structuralness where the argument of ‘Structural’ is something like a grammatical category rather than a linguistic  expression.[8]  Most importantly, Sider does not have higher order quantification, so his regimentation of ‘Conjunction is perfectly natural’ does not extend to claims like ‘Conjunction is the only perfectly natural binary operator’.