These two kinds of genius require different and peculiar faculties. In philosophy, where the great end proposed is the discovery of truth, the coloring of imagination should be carefully avoided as useless and deceptive. It is necessary to divest the mind as far as possible of all pre-conceived opinions, that so the proofs presented may make just the impression which their character and importance demand. No prejudice or association of former ideas must be allowed to bias the judgment; but the question should be decided in strict accordance with the deductions of the sternest reason. And yet this perfect freedom from prejudice, however necessary to the proper use of right reason, is perhaps the most difficult effort of the human mind. "Nemo adhuc," says Lord Bacon, in a passage quoted by Stewart in the introduction to his mental philosophy, "Nemo adhuc tanta mentis constantia inventus est, ut decreverit et sibi imposuerit theorias et notiones communes penitus abolere, et intellectum abrasum et æquum ad particularia de integro applicare. Itaque illa ratio humana quam habemus ex multa fide et multo etiam casu, necnon ex puerilibus quas primo hausimus notionibus, farrago quædam est et congeries. Quod si quis, ætate matura et sensibus integris et mente repurgata, se ad experientiam et ad particularia de integro applicet, de eo melius sperandum est." Such was the opinion of the great father of modern philosophy. On the other hand these vulgar errors and superstitions, these "theoriæ et notiones communes," supply the means of producing the strongest effect of poetry. The dull scenes of real life can never be suffered to chill the ardor of a romantic imagination. And as the poet finds truth too plain and unadorned to satisfy his enthusiastic fancy, he is compelled to seek subjects and scenery of more faultless nature and brighter hues than this world affords. He delights in combinations of the most striking images. The grand and imposing, the dark and terrific, the furious and desolating--whatever serves to fill the mind with awe and wonder, are his favorite subjects of contemplation. The legends of superstition contribute largely to the effect of poetical composition. The enthusiast loves to fancy the agency of supernatural beings, and endeavors to feel the influence of those emotions which such a belief is suited to inspire. This seems to be the spirit of Collins in the following lines of his ode to fear. "Dark power, with shuddering meek submitted thought, Be mine to read the visions old Which thy awakening bards have told; And lest thou meet my blasted view, Hold each strange tale devoutly true."