The nearly missed bus

About this video

Nadia runs round the corner just as the bus is closing its doors, and jumps on, out of breath. "That was close," she thinks. "I nearly missed it." She didn't miss it, but she could have: her morning could have gone differently. Other things couldn't: whatever happened, two plus two would still have made four. What is the difference?

Something that could be, or could have been, is possible: Nadia missing the bus was possible; it didn't happen, but it could have. Something that couldn't be, however things went, is impossible: a circle that is also a square, a triangle with four sides. It isn't just that nobody has found one; the idea doesn't fit together. Something that must be, however things went, is necessary: two plus two make four, a triangle has three sides. No change in the world could make them otherwise.

People also call flying by flapping your arms impossible, but it is impossible in a different way from a square circle. You can picture someone flying - it happens in dreams and stories. The laws of nature rule it out; the idea itself doesn't. Philosophers keep these apart: what the laws of nature allow, and what could be at all.

But what makes "Nadia could have missed the bus" true? The missed bus never happened, so it can't be anything in the world. One answer: possibilities are ways of thinking about this world - nothing in the idea goes wrong, and nothing about Nadia or buses rules it out. Its puzzle: if determinism is true, everything about the world did rule it out. The other answer: every possibility is real somewhere. The American philosopher David Lewis argued in 1986 that every way the world could have been is a real world, as real as ours, though we can never visit it. Its puzzle: almost nobody can believe it - Lewis said people met it with "an incredulous stare". This video goes with the Could It Have Been Different? lesson of Metaphysics Level 1 on Knaph.

Transcript

1. 0:00Nadia jumps on the bus as the doors close. She nearly missed it.
2. 0:05Missing it was possible. A square circle is impossible. Two plus two is four, necessarily.
3. 0:11Flying by flapping is ruled out by nature's laws. A square circle, by the idea itself.
4. 0:17What makes she could have missed it true? A way of thinking about this world?
5. 0:23Or real worlds, said David Lewis. Most people stare in disbelief.
6. 0:29Could it have been different?