Consistent with the rules of logic.
A logical possibility can remain physically or practically impossible.
Side 117
Modality & Possible Worlds
A study of how philosophy represents what could be, must be, might have been and could not have been otherwise.
actual→possible→necessary→counterfactual→explanation
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Possibility and necessity come in different forms.
Modal claims are ambiguous unless the relevant constraints are stated.
Compatible with the laws of nature.
Physical possibility depends on which laws and boundary conditions are held fixed.
Compatible with what is known.
Something can be epistemically possible even if it is in fact impossible.
Available to an agent under real constraints.
Resources, institutions and capabilities narrow possibility beyond logic or physics.
Possible-world semantics represents modal structure comparatively.
A possible world can be treated as a way things might have been, but theories disagree about what such worlds are.
The way things in fact are.
Modal reasoning begins from actuality but is not restricted to it.
Relevant alternatives depend on an accessibility relation.
Different modal systems encode different assumptions about which alternatives count.
True across all relevant accessible worlds.
The strength of a necessity claim depends on the modal domain.
True in at least one relevant accessible world.
Existence of an alternative is weaker than probability or feasibility.
Counterfactuals compare actuality with nearby alternatives.
The phrase 'if X had happened' requires a rule for which differences are held fixed and which may change.
Choose alternatives that preserve relevant background facts.
There is no neutral measure of nearness; context determines what counts as a small departure.
Ask whether Y changes with X.
Counterfactual dependence is central to causal reasoning but is not identical to causation.
Decide whether antecedents revise earlier conditions.
Some counterfactuals invite changes to prior causes; others hold the past fixed.
Causal models formalize controlled changes.
Interventionist counterfactuals distinguish changing a variable from merely observing it.
Modal truth raises questions about essence and reality.
Semantics can model modal claims without settling what ultimately grounds their truth.
Some properties may belong to what a thing is.
Essentialist claims are stronger than claims about stable or typical properties.
Could this very object have been different?
Trans-world identity asks what makes an individual the same across alternatives.
What makes modal claims true?
Answers range from concrete worlds to abstract structures, essences and primitive modality.
A useful semantics need not dictate ontology.
Representational utility and metaphysical belief should be kept distinct.
Modal language expands beyond actuality. The discipline is to specify what kind of possibility is being claimed and what makes the claim true.