Overview

Modality deals with the mode in which things exist or are true. It distinguishes between what is (actual), what could be (possible), and what must be (necessary).

Core Idea

The core idea is alternatives. Reality is just one way things could have been. Modality explores the entire space of possibility.

Formal Definition

  • Necessary: True in all possible worlds (e.g., $2+2=4$).
  • Possible: True in at least one possible world (e.g., “I am wearing a red shirt”).
  • Contingent: True in the actual world, but could have been false.
  • Impossible: True in no possible worlds (e.g., “Square circle”).

Intuition

  • Possible Worlds: Imagine an infinite library of books. One book describes our universe exactly. Other books describe universes where dinosaurs didn’t die, or where gravity is repulsive.
  • Modal Realism: David Lewis argued these other worlds are real physical places, just disconnected from us.

Examples

  • Counterfactuals: “If I had dropped the glass, it would have broken.” This statement relies on modality (what would happen in a possible world).
  • Essentialism: Are there properties an object must have? (e.g., Could Socrates have been an alligator? Probably not. Being human is essential to him).

Common Misconceptions

  • Misconception: “Possible” means “likely.”
    • Correction: In philosophy, “possible” just means “not contradictory.” A universe made entirely of cheese is possible.
  • Misconception: Necessity is just about language.
    • Correction: Kripke argued for metaphysical necessity (e.g., Water is H2O) which is true independent of language.
  • Modal Logic: The formal system for reasoning about modality.
  • Ontology: Do possible worlds exist?
  • Causality: Often defined in terms of counterfactuals.

Applications

  • Science: Laws of nature are often seen as “nomologically necessary” (necessary given the laws of physics).
  • History: “What if” scenarios (Counterfactual history).

Criticism and Limitations

  • Epistemology: How do we know what is possible in other worlds? We can’t visit them. We rely on intuition, which is unreliable.

Further Reading

  • On the Plurality of Worlds by David Lewis
  • Naming and Necessity by Saul Kripke