Philosophers love necessity and contingency. Some things must be the case (mathematical truths, the laws of logic). Other things just happen to be the case (the number of planets, whether you had coffee this morning). This distinction is load-bearing. It’s not just a classification. It’s meant to tell us where explanation can and cannot go.
Necessary truths can explain things, but we don’t get to ask why they obtain. They’re the stopping points. Contingent truths, meanwhile, float free: they could have been otherwise, and that’s that. The modal classification does double duty. It describes the world and regulates inquiry.
This picture hides something important.
The Pattern
Look at how explanation actually works across different domains:
- Mathematics constrains physics. Certain physical states are ruled out because they’d violate mathematical truths. We don’t treat this as mysterious. It’s just how things work.
- Normative facts constrain rationality. That an action would be unjust explains why it’s not a genuine rational option. Again, no mystery.
In both cases, facts from one domain (mathematics, normativity) reach into another domain (physics, rational agency) and do explanatory work. We accept this without fuss.
But now try the reverse. Can physical facts explain why certain mathematical structures are realized? Can contingent features of the world explain anything about necessary truths? Here, philosophers balk. That direction of explanation is blocked.
Why? Not because anyone has shown that such explanations would be incoherent. Not because they’d fail to illuminate. The reason, when you push on it, is usually just modal: necessity can constrain contingency, but contingency can’t constrain necessity. The direction of explanation tracks the modal hierarchy.
The Firewall
I call this pattern a modal firewall. It’s a restriction on explanatory scope that’s justified by modal status rather than by anything about explanation itself. The firewall doesn’t show that a candidate explanation would fail. It rules the explanation out of bounds before we even try.
Here’s the structure:
1) Eligibility: The blocked explanation would, by ordinary standards, be perfectly intelligible.
2) Modal restriction: It’s excluded because of the domain-relative modal status of what’s being explained.
3) No independent grounding: No explanation for the modal boundary. It’s taken as given.
Firewalls aren’t arguments. They’re policies. And once you see them, you see them everywhere.
Why This Matters
The problem isn’t that explanation has to be unlimited. Some explanations fail; some inquiries terminate. That’s fine. The problem is how the limits are drawn. If a stopping point is justified by demonstrating that further explanation would be incoherent, circular, or regressive, fair enough. But if it’s justified by pointing at a modal classification and saying “Here be contingency.” That’s not an explanation of the limit. It’s a label for the limit.
This matters for the contingency/necessity debate because contingency is often sold as metaphysically innocent. The necessitarian (someone who thinks everything is necessary) is supposed to be the one with the weird, revisionary view. But if contingency’s main job is to license unexplained stopping points in our explanatory practices, that innocence starts to look questionable.
A Different Approach
The alternative I develop is what I call explanatory unity: let explanation go where it succeeds, and stop where it fails, without giving modal classification independent authority to police the boundaries. Domain differences might shape how we explain, but they don’t get to determine that explanation must stop.
This isn’t a commitment to explaining everything. It’s a commitment to earning your stopping points rather than inheriting them from a modal map drawn in advance.
Does this vindicate necessitarianism? Not directly. But it shifts the burden. If you want to say that contingency limits explanation, you need to explain why—not just assert that it does.
This is a compressed version of an argument developed at length in a paper currently under review. The full version applies the diagnostic to debates about grounding, laws of nature, essence, and normativity.
Papers on MOAN: the Modal Ontological Argument for Necessitarianism, and the Dilemma of Contingency are also under review. And a paper on Spinoza.
Petronius Jablonski 