 Regarding philosophy, Arnauld, like Descartes, held that its purpose was to acquire useful knowledge through reason. That reason ought to be employed only in the pursuit of useful knowledge is emphasized in the opening pages of the Logic. Arnauld and Nicole say that “speculative sciences, such as geometry, astronomy, and physics” can be used as instruments for perfecting judgment and reason. This provides a use for some of the “nooks and crannies” of those sciences, which would otherwise be “completely worthless.” They go on to say,