Kotzee and Smit explain why, if unicorns don't exist, then they could not possibly have existed. In fact, even if horned horses were discovered somewhere, they would not necessarily be unicorns. The key to understanding why this is so lies in understanding how so-called natural kind terms function.
Ben Kotzee is lecturer in the School of Continuing Education, Birkbeck College, University of London.
J.P. Smit is lecturer in philosophy at Stellenbosch University.