This book has issued from the throes of dissension and strife, seeing the light at a time when, in Austria and Germany, the bitter forces of opposition, that range themselves about the shibboleth _Freedom of Science_, were seen engaging in a combat of fiercer intensity than ever. Yet, notwithstanding, this Child of Strife has learned the language of Peace only. It speaks the language of an impartial objectivity which endeavours, in a spirit of unimpassioned, though earnest, calm, to range itself over the burning questions of the day—over those great _Weltanschauung_ questions, that stand in such close relation with the compendious motto: _Freedom of Science_. Yes, _Freedom_ and _Science_ serve, in our age and on both sides of the Atlantic, as trumpet-calls, to summon together—often indeed to pit in deadly combat—the rival forces of opposition. They are catch-words that tend to hold at fever-pitch the intellectual life of modern civilization—agents as they are of such mighty and far-reaching influences. On the one hand, Science, whence the moving and leading ideas of the time take shape and form to go forth in turn and subject to their sway the intellect of man; on the other, Freedom—that Freedom of sovereign emancipation, that Christian Freedom of well-ordered self-development, which determine the actions, the strivings of the human spirit, even as they control imperceptibly the march of Science. While the present volume is connected with this chain of profound problems, it becomes, of itself, a representation of the intellectual life of our day, with its far-reaching philosophical questions, its forces of struggle and opposition, its dangers, and deep-seated evils. The Author has a lively recollection of an expression which he heard a few years ago, in a conversation with an American professor, then journeying in Europe. “Here, they talk of tolerance,” he observed, “while in America we put it into practice.” The catch-word _Freedom of Science_ will not, therefore, in _every_ quarter of the world, serve as a call to arms, causing the opposing columns to engage in mutual conflict, as is the case in many portions of Europe. But certain it is that everywhere alike—in the new world of America, as well as in the old world of Europe—the human spirit has its attention engaged with the same identical questions—those topics of nerve-straining interest that sway and surge about this same catch-word like so many opposing forces. Everywhere we shall have those tense oppositions between sovereign Humanity and Christianity, between Knowledge and Faith, between Law and Freedom; everywhere those questions on the Rights and Obligations of Science, on Catholic Thought, and on Catholic Doctrinal Beliefs and Duties.