 As we have already seen in section 2, spacetime in GTR is dynamical. This leads Brown to maintain that there is no substantial conceptual distinction between the metric field of GTR and matter fields: “Gravity is different from the other interactions, but this doesn’t mean that it is categorically distinct from, say, the electromagnetic field” (Brown 2005, p. 159). In this sense, Brown is a relationist about GTR, and counts authors such as (Rovelli, 1997) as allies. However, much caution is needed concerning this use of the term ‘relationism’. In particular, in the context of GTR – and in significant contrast with his approach to theories such as STR – Brown makes no claim that the metric field should be ontologically reduced to properties of (the laws governing) matter fields; rather, in light of its dynamical status, the metric field of GTR “cries out for reification” (Brown, personal communication). Indeed, even if Brown did not maintain this, we have already registered above that there are technical problems with attempting to apply the dynamical approach, understood as a version of regularity relationism, to theories such as GTR.