The heavy emphasis on theoretical philosophy in Buddhism— heavier than in many other religions—may result from the general Indian devotion to philosophical investigation. This and the Indian tendency to explain philosophy in terms of religious practice influenced Buddhism considerably. Shakyamuni himself was especially interested in philosophical issues and would employ nothing in his teachings that was not theoretically convincing. After having made a thorough investigation of the doctrines of the religions and philosophies of his time in order to determine which were correct and perfect, he compiled the distinctive teachings like the Law of Causation that distinguish Buddhism from other religions. Consequently, Buddhism has a rational foundation enabling it to withstand any criticism on the theoretical plane. Its rationalism is not concerned solely with abstract truth for its own sake but is a basis for actual practice of religious faith. This means that Buddhist faith is not merely unfounded enthusiasm but practical faith with a firm rational and ethical basis. Buddhist theory and practice are one. In Buddhism there is no theory that does not take practice into consideration, and there is no practice lacking theoretical substantiation. (Page 159)