Identity across possible worlds
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Identity across possible worlds | |
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| Type | Metaphysical problem |
| Field | Metaphysics |
| Core idea | Question of how entities can be identified across alternative possible circumstances |
| Assumptions | Identity conditions can extend beyond actuality; cross-world comparison is meaningful |
| Status | Contested |
| Related | Identity; Possible worlds; Essentialism; Modality |
Identity across possible worlds is a metaphysical problem concerning how, or whether, an entity in one possible world can be identified with an entity in another possible world. The issue arises when reasoning about what an entity could have been like under alternative circumstances.
The problem is central to debates about identity, essentialism, and modal reasoning.
Core idea
At its core, the problem asks what it means to say that an entity in a non-actual scenario is the same entity as one in the actual world. When considering alternative possibilities, it is unclear what grounds identity across worlds.
This question challenges intuitive notions of sameness.
Identity and modality
Identity across possible worlds connects identity to modality. Modal claims about what an entity could have been presuppose some way of tracking that entity across alternatives.
Without such tracking, modal claims about individuals lose clear meaning.
Essential properties
One common approach appeals to essential properties. If an entity has properties that are necessary to its identity, those properties can serve as criteria for identifying it across possible worlds.
This approach aligns with essentialism.
Counterpart relations
An alternative approach denies strict identity across worlds. Instead, entities in different worlds are related by similarity or counterpart relations rather than identity.
On this view, talk of what an entity could have been is understood as talk about similar entities in other worlds.
Actualism
Some positions restrict existence to the actual world and treat possible worlds as abstract representations. Under such views, identity across worlds is analyzed in representational terms rather than as literal cross-world identity.
This avoids commitment to non-actual entities.
Problems of arbitrariness
Determining which entity in another world corresponds to an actual entity can appear arbitrary. Similarity judgments may vary depending on which features are emphasized.
This raises concerns about the objectivity of cross-world identity claims.
Identity and essence
Debates about identity across possible worlds often hinge on which properties are taken to be essential. Disagreement about essence leads to disagreement about identity conditions.
This interdependence complicates modal analysis.
Applications
Identity across possible worlds is relevant to discussions of necessity, counterfactuals, and moral responsibility. Claims about what an agent could have done presuppose some notion of cross-world identity.
The problem also arises in metaphysical interpretations of modal logic.
Limits and disagreement
There is no consensus on how identity across possible worlds should be understood. Some deny that strict identity across worlds is coherent, while others treat it as indispensable for modal reasoning.
These disagreements reflect deeper metaphysical commitments.
Status
Identity across possible worlds is a central and unresolved problem in metaphysics. Its analysis clarifies how identity, possibility, and necessity interact in modal reasoning.