Transcendentalism was a direct response and reaction to the ideas of Deism and "rational religion" that had arisen from Enlightenment ideas. Among these groups were the Unitarians and the Universalists, who said that Reason and logic were more important than creeds or religious doctrine, much less the idea that the Bible was infallible.
Transcendentalism emphasized the idea that some things could not be explained on the basis of reason and logic alone. To quote an expert on the subject, "Transcendentalism assumed certain fundamental truths not derived from experience, not susceptible of proof, which transcend human life and are perceived directly and intuitively by the human mind." The primary European thinker was Immanuel Kant, who said that logic and reason alone were not enough to explain things. Among the American thinkers were Ralph Waldo Emerson, the author of Self Reliance, and Henry David Thoreau. All Transcendentalist thinkers emphasized that one should follow his own conscience. Thoreau opposed the Mexican War, as he considered it a war to advance slavery, and once commented, "If the law is of such a nature that it requires you to be an agent of injustice to another, then I say, break the law."