Enthusiasm (ἐνθουσιασμός from ἔνθεος, inspired; God-possessed; rapt) is used both in a good and a bad sense.
1. In the first, which springs from its derivation, it signifies divine inspiration in general; or, secondarily, any extraordinary mental or moral exaltation. "The raptures of the poet, the deep meditations of the philosopher, the heroism of the warrior, the devotedness of the martyr, and the ardor of the patriot, are so many different phases of enthusiasm." In this sense it "is almost a synonyme of genius; the moral life in the intellectual light, the will in the reason; and without it, says Seneca, nothing truly great was ever achieved" (Coleridge). "There is a temper of mind called enthusiasm, which, though rejecting the authority neither of reason nor of virtue, triumphs over all the vulgar infirmities of men, contemns their ordinary pursuits, braves danger, and despises obloquy, which is the parent of heroic acts and devoted sacrifices, and which devotes ease, pleasure, interest, ambition, and life to the service of one's fellow-men" (Mackintosh, Miscellaneous Works, London 1851, page 731).
2. The bad sense of the word was formerly in much more common use than now. According to it, an enthusiast is one who substitutes his own fancies for reason and truth, especially in matters of religion. "Every enthusiast is properly a madman; yet his is not an ordinary, but a religious madness. The enthusiast is generally talking of religion, of God, or of the things of God, but talking in such a manner that any reasonable Christian may discern the disorder of his mind. Such enthusiasm may be described, in general, as a religious madness arising from some falsely imagined influence or inspiration of God; at least, from imputing something to God which ought not to be imputed to him, or expecting something from God which ought not to be expected from him" (Wesley, Sermon on Enthusiasm, Works, 2:331 sq.). Warburton similarly defines enthusiasm as "that temper of mind in which the imagination has got the better of the judgment" (Div. Leg. book 5, Appendix). James Blair (Sermons, 1740, 4:274) makes religious enthusiasm to consist especially in "' setting up the private spirit to assert anything contrary to Scripture." So Waterland (Works, Oxford, 1843, 4:422) says that "enthusiasm, in the bad sense, is a subtle device of Satan upon ill-meaning or unmeaning instruments, making use of their ambition, self-admiration, or other weakness, to draw them by some plausible suggestions into a vain conceit that they have something within them either of equal authority with Scripture, or superior to it." On the stupid misapplication of the term enthusiasm by worldly men to designate true Christian life, see Wesley's sermon above, and also Taylor, Natural Hist. of Enthusiasm (N.Y. 1834, 4th ed. 12mo).