The perception of some Indians that modern Western thought provided the key to the regeneration of their society can be attributed to several factors. These factors include the influence of modern science, the appeal of doctrines of reason and humanism, and the demands for modernization from different segments of Indian society.

1. Modern Science:
One reason why some Indians felt that modern Western thought could regenerate their society is the impact of modern science. The advancements and achievements in scientific fields such as technology, medicine, and industry impressed many Indians. They recognized the practical benefits and progress that modern science brought to Western societies and believed that adopting these scientific methods and principles could lead to the development and improvement of their own society.

2. Doctrines of Reason and Humanism:
The doctrines of reason and humanism, which were prominent in Western thought, also appealed to some Indians. These doctrines emphasized the importance of rational thinking, critical inquiry, and the promotion of human welfare and rights. Indians who were influenced by these ideas saw them as a potential solution to the social, economic, and political challenges facing their country. They believed that embracing these principles could lead to the transformation and regeneration of Indian society.

3. Demand for Modernization:
Another reason why some Indians looked to Western thought for regeneration was the demand for modernization from various segments of society. The capitalist class, the working class, and the modern intelligentsia recognized the need for modernization in order to advance their own interests. The capitalist class sought industrialization and economic growth, the working class sought better working conditions and improved standards of living, and the modern intelligentsia sought intellectual progress and societal reforms. These groups saw Western thought and practices as a means to achieve their goals and therefore advocated for the adoption of Western ideas and methods.

In conclusion, the perception of some Indians that modern Western thought provided the key to the regeneration of their society was influenced by the impact of modern science, the appeal of doctrines of reason and humanism, and the demands for modernization from different segments of Indian society. These factors collectively led some Indians to believe that adopting Western ideas and practices could bring progress and development to their own society.