Answer :

Gibbs
During the enlightenment era and also during the classical period major philosophers believed that a dependable guide to human thinking was reason and logic. By using reason and logic and also principles of humanism humans were capable of guiding their thinking effectively. 

Answer:    Reason

Explanation:  The Enlightenment era meant the rejection of the acceptance of knowledge on the basis of faith, and promoted reason as the basic criterion of cognition. This reflected not only the relationship to the Church but also the system of government, the scientific approach and the analysis of all phenomena in nature. Natural laws are not meant to reject religion, but to reject Church teaching, and religion was understood by reason and by study of the laws of nature. According to the Enlightenment, the laws of nature are those which people have dealt with, as present in nature and in society, and subject to reasonable analysis and examination.