 The ultimate aim of the method is constructive. Unlike “the sceptics, who doubt only for the sake of doubting,” Descartes aims “to reach certainty – to cast aside the loose earth and sand so as to come upon rock or clay” (Discourse 3, AT 6:29, CSM 1:125). Bulldozers are typically used for destructive ends, as are sceptical doubts. Descartes’ methodical innovation is to employ demolition for constructive ends. Where a bulldozer’s force overpowers the ground, its effects are destructive. Where the ground’s firmness resists the bulldozer’s force, the bulldozer might be used constructively – using it to reveal the ground as firm. Descartes thus uses sceptical doubts to test the firmness of candidates put forward for the foundations of knowledge.