The philosophy of the eighteenth century Enlightenment in England and Europe was characterized by trust in reason, the elevation of the individual, the questioning and reform of religious, political, and social institutions, and more rigorous methods of scientific inquiry than had been practiced earlier. It emphasized progress, the improvement of society and of the individual, and tolerance. Enlightenment philosophers refused to accept tradition and authority on faith, thus paving the way for the later rise of Unitarianism in America and setting the stage for the subsequent Transcendental rebellion. But heirs though they were to this philosophical examination and evaluation of established beliefs and institutions, the New England Transcendentalists departed radically from their rationalist predecessors in their approach to the nature of knowledge and human understanding.
(English philosopher John Locke 1632–1704) was a major influence on the Enlightenment. Locke addressed many subjects, religion, politics, and society among them. In his epistemology (theory on the nature of knowledge), Locke had a significant impact on Transcendentalism, which arose partly in reaction to his philosophy. Locke asserted that ideas originated in the physical transmission of sensations to the tabula rasa — the blank slate — of the mind. In his Essay Concerning Human Understanding (1690), he declared that all ideas capable of conscious understanding were derived from experience in its interaction with human physiology.
For Locke, the human mind at birth was devoid of conscience, moral understanding, and intuition, all of which developed through experience. He rejected the notion that a sense of God and of moral law was innate. Locke equated the process by which religious and moral concepts were understood with the process by which mathematics and the sciences were understood. Religious perception was essentially a material, not an idealistic, process. It did not transcend the physical world. Locke's rationalism appealed to the American Unitarians as they struggled to throw off the negative view of human nature held by their Calvinistic forebears. As the Transcendentalists were defining religious understanding for themselves, however, they were repelled by Locke's materialism and eager to embrace a more idealistic model of the human mind, one that would permit an innate understanding of God and morality. During the "miracles controversy" of the 1830s and 1840s, Locke's theory guided Unitarian leaders in viewing the New Testament miracles as empirically understandable evidence of Christianity, an approach that the Transcendentalists could not accept.
The Transcendentalists found the ideas of German philosopher Immanuel Kant (1724–1804) more satisfying. In his theory of knowledge, Kant distinguished between the world of sense and that of understanding. He believed that sensory experience revealed things as they appeared, but understanding revealed them as they were. In his Critique of Pure Reason (1781) and his Critique of Practical Reason (1788), Kant asserted that there were aspects of knowledge — God, morality, freedom, and immortality, for example — that could not be understood by reason, but that were rather innate within man and understood intuitively. The human mind was not the tabula rasa that Locke had claimed it was. Man was a fundamentally moral and godly being. The understanding of such ideas was transcendental — it transcended sensation and reason. Although the modern reader may be unaccustomed to pondering such philosophical concepts, an understanding of the differences between sensationalism (materialism) and idealism (transcendence) was central to Transcendental philosophy. The Transcendentalists recognized their debt to Kant and understood the points on which Kant and Locke disagreed. Emerson, in his 1841 lecture "The Transcendentalist," provided the following summary:
It is well known to most of my audience, that the Idealism of the present day acquired the name of Transcendental, from the use of that term by Immanuel Kant, of Königsberg, who replied to the skeptical philosophy of Locke, which insisted that there was nothing in the intellect which was not previously in the experience of the senses, by showing that there was a very important class of ideas, or imperative forms, which did not come by experience, but through which experience was acquired; that these were intuitions of the mind itself; and he denominated them Transcendental forms. The extraordinary profoundness and precision of that man's thinking have given vogue to his nomenclature, in Europe and America, to that extent, that whatever belongs to the class of intuitive thought, is popularly called at the present day Transcendental.
All else that came under the heading "New England Transcendentalism" was predicated on the acceptance of Kant's view of the nature of knowledge.
The Transcendentalists read the writings of both Locke and Kant. Locke's work was part of their Unitarian heritage and the college curriculum of the era. As for Kant, some of the Transcendentalists — Frederic Henry Hedge and Theodore Parker, for example — were able to read his work in the original German. Others, including Emerson, read Kant in English translation. The ideas of Kant and other intuitive philosophers were also disseminated through the writings of British and French authors. In his emphasis on spirituality, intuition, and imagination, British poet-philosopher Samuel Taylor Coleridge was influenced by Kant and, in turn, influenced the Transcendentalists. The "Preliminary Essay" to James Marsh's 1829 edition of Coleridge's Aids to Reflection elaborated upon the difference between intuitive and sensational knowledge (from the modern point of view, somewhat confusingly termed Reason — but not in the Enlightenment meaning of reason — and Understanding, respectively). Scottish-born essayist and biographer Thomas Carlyle, highly regarded by the Transcendentalists, celebrated intuition over rationality and wrote about Goethe, Kant, Novalis, Richter, Schiller, and other German thinkers. French philosopher Victor Cousin both espoused idealistic philosophy and also interpreted Kant and other German philosophers for a general audience.