 Two philosophers who did acknowledge the importance of scepticism for philosophy were  G. W. Leibniz (1646–1716)  and  G. W. F. Hegel (1770–1831;  1801 [1985]). As a matter of fact, in response to a letter by French mathematician, Pierre Varignon (1654–1722), who had asked him for some clarification on what he meant by “infinitesimal”, Leibniz reference’s Sanches’ Quod nihil scitur and his challenge to Clavius with some admiration. Such scepticism, he says to Varignon, is important because it keeps mathematics from becoming a dogmatic science (cf. de Olaso 1987: 149–150). The questions raised by sceptics like Sextus Empiricus and Sanches, says Leibniz, are key for “establishing sound foundations for a science” ([1702 [1970: 544]). Leibniz writes: 