Ralph Waldo Emerson, Margaret Fuller, and Henry David Thoreau were all Romantic artists. social reformers. religious revivalists. transcendentalist thinkers.

The right answer is the last one: transcendentalist thinkers. Transcendentalism was a philosophical, religious and literary movement that originated in the US (specifically as a reform movement within the Unitarian Church) approximately between 1836 and 1860. Based on Romanticism, Hinduism and Rationalism, transcendentalist thinkers believed in the capacity of each individual consciousness (without the need of religious mediators or ideas), in his/her purity, independence and self-reliance, which society and its institutions have corrupted.