Like the water in a lake, the pool of understanding can also evaporate again – for what we think we understand today can be exposed as nonsense tomorrow, just as what we thought we understood yesterday is exposed as nonsense today. We use the word ‘understanding’ rather than ‘knowledge’ because science is both more than and less than a collection of immutable facts.

– on understanding |
Terry Pratchett, Ian Stewart, and Jack Cohen, The Science of Discworld III: Darwin’s Watch