A familiar kind of explanation has become increasingly common in contemporary physics communication. A question is posed in ontological form—Why does X exist?—and answered with a confident theoretical dependency: Because Y exists, where Y names a structural feature of our best theory.
The explanation is often correct. It is also often misunderstood.
This post is about that misunderstanding. More precisely, it is about how theoretical necessity comes to be heard as ontological explanation, and how constraints begin to sound like causes.
Two Kinds of “Why”
The word why does more than one job.
Sometimes it asks for a dependency within a framework:
Given these assumptions and constraints, what follows?
At other times it asks for an account of the framework itself:
Why this structure of possibility rather than another?
These are not rival questions. They belong to different levels of inquiry. Trouble begins when an answer to the first is taken to have settled the second.
The Power of Theory-Internal Explanation
Modern physics is extraordinarily good at explaining why certain phenomena are unavoidable once a particular theoretical structure is adopted. When a theory specifies a constrained space of possible states, symmetries, or transformations, it often follows that certain entities or processes must appear.
These explanations are compelling because they are non-arbitrary. They do not say merely that something happens to exist, but that it could not have been otherwise, given the constraints.
Within the theory, this is exactly right.
But the necessity here is conditional, not absolute. It is a necessity relative to a chosen construal of physical possibility.
Constraint Is Not Cause
The slide from theory to ontology often occurs through a subtle grammatical shift. Constraints are described in causal language:
“This symmetry produces that phenomenon.”
“This structure explains the existence of that entity.”
Yet constraints do not produce anything. They delimit what counts as a coherent instance within a system. They tell us not what happens, but what can happen intelligibly.
A constraint is not an agent. It does not act. It enables.
To mistake constraint for cause is to mistake the conditions of intelligibility for mechanisms in the world.
The Feeling of Metaphysical Closure
Why is this mistake so tempting?
Because constraint-based explanations feel deeper than causal ones. They do not merely track sequences of events; they reveal the architecture of possibility. When a phenomenon turns out to be unavoidable given a small number of structural assumptions, it can feel as though reality itself has been laid bare.
But what has been revealed is the internal economy of a theory.
The sense of closure comes from the success of the construal, not from having reached beneath construal altogether.
What the Explanation Really Says
When a physicist says that a phenomenon exists because a certain symmetry or structural feature exists, the disciplined reading is this:
Once physical possibility is organised in this way, phenomena of this kind are unavoidable.
That is a strong claim. It is also a limited one.
It does not tell us:
why physical possibility is organised that way,
why that construal rather than another is realised,
or why there is a structured space of possibilities at all.
Those questions have not been answered. They have simply not been asked at that level.
No Critique of Physics Intended
Nothing in this diagnosis undermines the physics. On the contrary, it depends on taking theory seriously—seriously enough to respect its scope.
Physics earns its authority by doing exactly what it does so well: articulating constraints, mapping structured possibilities, and showing what must follow once those constraints are in place.
Problems arise only when the success of this enterprise is taken to license an answer to questions it was never designed to address.
Ontological Responsibility Revisited
To insist on this distinction is not to demand more from physics. It is to ask for clarity about what kind of work is being done when we explain.
An explanation can be:
complete within a construal,
decisive given its constraints,
and still silent about ontology.
Owning that silence is a form of responsibility, not a failure.
Living with the Distinction
Once the distinction between constraint and cause is kept in view, a great deal of confusion dissolves. We can admire the depth of our theories without mistaking their internal necessities for metaphysical ultimates.
We gain something in return: a clearer sense of where explanation ends and participation begins; where physics speaks, and where questions about reality require us to acknowledge the cuts we are making.
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