CARTESIAN, adj. Relating to Descartes, a famous philosopher, author of the celebrated dictum, _Cogito ergo sum_ --whereby he was pleased to suppose he demonstrated the reality of human existence. The dictum might be improved, however, thus: _Cogito cogito ergo cogito sum_ --"I think that I think, therefore I think that I am;" as close an approach to certainty as any philosopher has yet made.