In this paper, we explore the consequences of a flat ontology for planning theory and practice through the lens of Evolutionary Governance Theory (EGT). We present a perspective in which the ontological hierarchies assumed in planning and beyond are left behind, but also one that allows for understanding how hierarchies and binaries can emerge from and within governance and specifically planning. From this perspective, planning is conceptualised as a web of interrelated social-material systems underpinning the coordination of policies and practices affecting spatial organisation. Within this web, different planning perspectives and planning practices co-exist and co-evolve, partly in relation to the wider governance contexts of which they are part. We explore and deepen our understanding of the consequences of flat ontology by focussing on the interrelations between power and knowledge and the varied effects of materiality on planning and governance, as materiality can play roles ranging from latent infrastructure to main triggers of change. We conclude our paper by assessing the consequences for the positionality of planning in society, stressing the need for more reflexive and adaptive forms of planning and governance, and reflecting on what such forms of planning could look like. We argue that despite the abstract nature of discussions on ontology in and of planning, the conceptual shifts that result from thinking in terms of flat ontologies can significantly affect planning practices as it can inspire new ways of observing and organising.