There is no such thing as absolute certainty, but there is assurance sufficient for the purposes of human life.
John Stuart Mill, On Liberty
He seems to have understood that 0 and 1 are not probabilities.
You know, that post is somewhat annoyingly titled. 0 and 1 are probabilities by the common definition of "probability", but defining "probability" such that 0 and 1 are not probabilities results in a system which is also consistent and useful.
This is our monthly thread for collecting these little gems and pearls of wisdom, rationality-related quotes you've seen recently, or had stored in your quotesfile for ages, and which might be handy to link to in one of our discussions.