The cardinal point, then, of Sir W. Hamilton's philosophy, expressly announced as such by himself, is the absolute necessity, under any system of philosophy whatever, of acknowledging the existence of a sphere of belief beyond the limits of the sphere of thought. "The main scope of my speculation,"[Q] he says, "is to show articulately that we _must believe_, as actual, much that we are unable (positively) _to conceive_ as even possible." It is, of course, beyond the range of such a speculation, by itself, to enter on an examination of the positive evidences in support of one form of belief rather than another. So far as it aims only at exhibiting an universal law of the human mind, it is of course compatible with all special forms of belief which do not contradict that law; and none, whatever their pretensions, can really contradict it. Hence the service which such a philosophy can render to the Christian religion must necessarily, from the nature of the case, be of an indirect and negative character. It prepares the way for a fair examination of the proper evidences of Christianity, by showing that there is no ground for any _a priori_ prejudice against revelation, as appealing, for the acceptance of its highest truths, to faith rather than to reason; for that this appeal is common to all religions and to all philosophies, and cannot therefore be urged against one more than another. So far as certain difficulties are inherent in the constitution of the human mind itself, they must necessarily occupy the same position with respect to all religions alike. To exhibit the nature of these difficulties is a service to true religion; but it is the service of the pioneer, not of the builder; it does not prove the religion to be true; it only clears the ground for the production of the special evidences. [Q] Letter to Mr. Calderwood. See _Lectures_, vol. ii, p. 534.