When I say that God is an hypothesis, I run the risk of exciting, in many of you, feelings of astonishment not unmixed with pain. But I must beg you to remember the nature of these lectures. We are here far from the calm retirement of the sanctuary, and from such words of solemn exhortation as flow from the lips of the religious teacher. I have introduced you to the ardent conflicts of contemporary thought, and into the midst of the clamors of the schools. The soul which is seeking to hold communion with God, and so from their fountain-head to be filled with strength and joy, has something better to do than to be listening to such discourses as these. Solitude, prayer, a calm activity pursued under the guidance of the conscience,--these are the best paths for such a soul, and the discussions in which we are now engaged are not perhaps altogether free from danger for one who has remained hitherto undisturbed in the first simplicity of his faith. But we are not masters of our own ways, and the circumstances of the present times impose upon us special duties. The barriers which separate the school and the world are everywhere thrown down. Everywhere shreds of philosophy, and very often of bad philosophy,--scattered fragments of theological science, and very often of a deplorable theological science,--are insinuating themselves into the current literature. There is not a literary review, there is scarcely a political journal, which does not speak on occasion, or without occasion, of the problems relating to our eternal interests. The most sacred beliefs are attacked every day in the organs of public opinion. At such a juncture, can men who preserve faith in their own soul remain like dumb dogs, or keep themselves shut up in the narrow limits of the schools? Assuredly not. We must descend to the common ground, and fight with equal weapons the great battles of thought. For this purpose it is necessary to make use of terms which may alarm some consciences, and to state questions which run the risk of startling sincerely religious persons. But there is no help for it, if we are to combat the adversaries on their own ground; and because it is thus only that, while we startle a few, we can prove to all that the torrent of negations is but a passing rush of waters, which, fret as they may in their channel, shall be found to have left not so much as a trace of their passage upon the Rock of Ages.