In Praise of Post-Its

They have made an incalculable difference to intellectual life, pushing at the boundaries of human ignorance. How was research possible without them – or systematic thought? One is led to speculate: did Aristotle's edition of Plato flash with pale yellow? did Leonardo make a blueprint for the post-it note, beside the helicopter and a sketch of the Mona Lisa? Wittgenstein once wrote (to Gilbert Pattison) that he would like to "card-index" his mind. Thanks to Romy and Michelle, this is finally possible.