‘If a single flap of a butterfly’s wings can be instrumental in generating a tornado, so also can all the previous and subsequent flaps of its wings, as can the flaps of the wings of millions of other butterflies, not to mention the activities of innumerable more powerful creatures, including our own species.’   

‘If the flap of a butterfly’s wings can be instrumental in generating a tornado, it can equally well be instrumental in preventing a tornado.’

Edward Lorenz, ‘Predictability: Does the Flap of a Butterfly’s wings in Brazil Set Off a Tornado in Texas?’, paper presented at the Global Atmospheric Research Program Conference,  Boston, December 1972