This Chapter offers no more than a tentative and imperfect outline of the theology of St. Hilary; it is an essay, not a monograph. Little attempt will be made to estimate the value of his opinions from the point of view of modern thought; little will be said about his relation to earlier and contemporary thought, a subject on which he is habitually silent, and nothing about the after fate of his speculations. Yet the task, thus narrowed, is not without its difficulties. Much more attention, it is true, has been paid to Hilary’s theology than to the history of his life, and the student cannot presume to dispense with the assistance of the books already written Those which have been in constant use in the preparation of this chapter have been an excellent article by Th. Förster in the Theologische Studien und Kritiken for 1888, p. 645 ff., and two full and valuable papers by Dr. Baltzer on the Theologie and Christologie of Hilary in the Programm of the Rottweil Gymnasium for 1879 and 1889 respectively. I have unfortunately not had access to Wirthmüller’s work, Die Lehre d. hl. Hil. über die Selbstentäusserung Christi, but the citations in Baltzer and Schwane give some clue to its contents. The Introduction to the Benedictine edition is useful, though its value is lessened by an evident desire to make Hilary conform to the accepted opinions of a later age. Dorner’s great work on the Doctrine of the Person of Christ, in the English translation, with the Dogmengeschichte of Schwane (ed. 2, 1895) and that of Harnack (ed. 3, 1894) have also been constantly and profitably consulted. Indebtedness to other works is from time to time acknowledged in the notes.. But they cannot release him from the necessity of collecting evidence for himself from the pages of Hilary, and of forming his own judgment upon it, for none of them can claim completeness and they differ widely as to the views which Hilary held. There is the further difficulty that a brief statement of a theologian’s opinions must be systematic. But Hilary has abstained, perhaps deliberately, from constructing a system; the scattered points of his teaching must be gathered from writings composed at various times and with various purposes. The part of his work which was, no doubt, most useful in his own day, his summary in the De Trinitate of the defence against Arianism, is clear and well arranged, but it bears less of the stamp of Hilary’s genius than any other of his writings. His characteristic thoughts are scattered over the pages of this great controversial treatise, where the exigencies of his immediate argument often deny him full scope for their development; or else they must be sought in his Commentary on St. Matthew, where they find incidental expression in the midst of allegorical exegesis; or again, amid the mysticism and exhortation of the Homilies on the Psalms. It is in some of these last that the Christology of Hilary is most completely stated; but the Homilies were intended for a general audience, and are unsystematic in construction and almost conversational in tone. Hilary has never worked out his thoughts in consistent theological form, and many of the most original among them have failed to attract the attention which they would have received had they been presented in such a shape as that of the later books of the De Trinitate.