Card 1.6.1 · Root I — Metaphysics
Possible Worlds
When you say something could have gone differently, what are you talking about?
Possible worlds are complete ways things might have been, used to give precise sense to claims about necessity, possibility and what would have happened.
Where it sits
Under 1.6 Modality. Feeds 4.3 Modal logic. Borders 1.4.2 Causation, 6.10.1 Reference.
The rival answers
| Position | Possible worlds are | The cost |
|---|---|---|
| Modal realism | Concrete, as real as this one, causally isolated | If isolated, we cannot know anything about them |
| Ersatzism | Abstract representations — sets of propositions or states of affairs | Must explain what makes a representation possible without using modality |
| Actualism | Maximal states of affairs, existing but uninstantiated | Same difficulty, differently located |
| Fictionalism | A useful fiction, like a map's legend | Then modal claims are not literally true |
| Combinatorialism | Recombinations of actual elements | Cannot generate genuinely alien possibilities |
Key figures
| Figure | Dates | Tradition | Contribution |
|---|---|---|---|
| Duns Scotus | c. 1266–1308 | Scholastic | Synchronic possibility — alternatives at a single moment |
| G. W. Leibniz | 1646–1716 | European modern | Possible worlds as ideas in the divine mind |
| Saul Kripke | 1940–2022 | Analytic | Possible-worlds semantics; worlds stipulated, not discovered |
| David Lewis | 1941–2001 | Analytic | Modal realism; other worlds concrete |
| Alvin Plantinga | b. 1932 | Analytic | Actualism; worlds as maximal states of affairs |
| Robert Stalnaker | b. 1940 | Analytic | Worlds as ways things might have been, not places |
Connections
→ 1.6 · ↔ 4.3, 1.4.2, 6.10.1, 1.1.4 · ◇ modal realism, ersatzism, actualism, fictionalism · ○ Scholastic; Modern; Table 1
→ narrower questions · ↔ questions it borders · ◇ the positions, mapped in Part III of the book · ○ the eras and comparison tables (Parts IV and V)
The full card is in the book
In The Coordinates of Thought this card goes on to a worked example that sets the answers against one case, and to where the question touches daily life — page 68.
On Coordinates of Thought
Conversations about this question in Possibility & necessity:
- S5 is the right logic for metaphysical necessity 6 replies
- Reading group: David Lewis, On the Plurality of Worlds (1986), chapters 1–4 6 replies
- Reading group: Epictetus, Discourses II.19, where the Master Argument meets a bus driver 5 replies
- Possibility lives in the powers of real things, not in other worlds 5 replies
- The incredulous stare is a perfectly respectable argument against modal realism 5 replies
Join free to ask about it Everything in Possibility & necessity