Was Rousseau a rationalist? This question can not fail to embarrass all those who have read his work thoughtfully. In reply to this question, the author takes up the problem as a whole. He does not content himself with analysing Rousseau’s texts, but compares them with historical antecedents and with the theories they are intended to refute. The conclusion shows the sense in which Rousseau, notwithstanding his appeal to sentiment, occupies a place in the rationalistic current of thought.