A stack is layers where each rests on the one below: a tech stack, rock strata, floors in a building. The reality stack turns “is this just the way things are?” into “which layer does this sit at, and therefore how contingent, how mutable, and how accountable is it?” It is not metaphysics but a teaching device, descriptive in form and normatively motivated: it exists to make a particular claim about inequality arguable.
The physical layer is invariant law: gravity, thermodynamics, the speed of light. You cannot negotiate with it; it gives rise to everything above without determining it.
The material layer is the physical world in the mode of human encounter: bodies, biology, climate, geography, and the infrastructure built into them. Not philosophical materialism, but physics seen through what humans need, are stuck with, and have made: the calorie requirement of a body, the river that is here and not there, the concrete a city is made of.
The social layer is constructed: arrangements humans make collectively, constrained by the material but not determined by it. Two societies with identical material conditions can organise themselves in opposite ways, and historically have. It is where power, roles, norms, and institutions live, and the layer people most often mistake for one below. Which side of the road you drive on, marriage, money.
The agent is not a fourth layer but a cross-section, a point where all three meet: a physical body, material needs, and a social layer carried inside as language, shame, politeness. What is purely agent? Very little: a flinch, a refusal. Yet the cross-section is the only site from which any of it can be questioned. Agents together reshape the social, which reshapes the material, which reshapes what is possible.
To test where something sits, ask: if the other layers varied independently, would this vary with them, or hold constant? Gravity holds across all societies and bodies (physical). A body’s calorie requirement holds across societies but varies across species (material). Which side of the road cars drive on varies across societies under identical material conditions (social). The test is not a decision procedure: gender, race, disease, addiction pass it ambiguously, and that is the point: the framework surfaces the dispute rather than resolving it.
This is why we distrust the word natural: it often smuggles a social claim down to the physical layer, where it can no longer be argued with. “Hierarchy is natural” makes hierarchy a law of gravity; “it is human nature to be selfish” relocates a collective behaviour to physics against the anthropological evidence. The word has honest uses; the suspicion is of the move: a way to escape accountability by crossing into a layer where accountability does not apply.
Three spectrums run through the stack. Contingency, whether it could have been otherwise: zero at the physical, some at the material, a great deal at the social. Mutability, how readily it changes: gravity never, material conditions over generations, social arrangements within a lifetime, an agent’s position in a moment. Accountability, not “who caused it” but “who, going forward, is situated to change it”; responsibility can be collective and forward-looking even when no individual chose the outcome. They come apart, and the interesting political arguments are always about which axis a dispute is on.
So when you catch yourself asking “is this just the way things are?”, locate the thing in the stack. If it sits at the physical layer, accept it. If it sits anywhere above, the question has an answer: it is this way because of the layer it sits at, the path it took, and the feedback that locked it in. None of that is destiny. That is the whole point of naming the layers.