Definition
Possibilism is Hans Rosling's coined word for the disposition between optimism and pessimism: the view that things can be both bad and getting better at the same time, and that the world has both serious remaining problems and a real record of progress to build on.
Optimism risks complacency — if things are fine, no work is needed. Pessimism risks paralysis — if things are doomed, no work is worthwhile. Possibilism splits the difference by holding two claims simultaneously: the current level is unacceptable, and the trend is moving in the right direction. Both are reasons to keep working.
Why it matters
How it works
The disposition operates on two questions instead of one. Where conventional debate asks "are things good or bad?", possibilism asks "what is the current level?" and "what is the direction of change?" The answers are usually independent: a country can have high child mortality (level: bad) and rapidly falling child mortality (direction: improving), or low corruption (level: good) and worsening corruption (direction: bad).
The two-question habit prevents both errors that purely-mood frameworks produce. It blocks the optimist's tendency to forgive a bad level because the trend is positive. It blocks the pessimist's tendency to dismiss a positive trend because the level is still bad. The resulting stance is awkward in slogans and accurate in policy.
Possibilism is the affective home of factfulness. Once the dramatic instincts have been caught and the worldview corrected, the corrected picture usually shows a world where most things are difficult and many are getting better. Possibilism is the disposition that takes that picture at face value and treats it as a working brief rather than a contradiction.