The universe presents itself to sense and sense-perception as a perpetual genesis, "a vast aggregation and history of phenomena conditioned in time and space which, by its diversity and mutability, is disqualified from being regarded as independent and self-existent." To our experiential knowledge, to our physical science in its highest generalizations, the universe is a product, an _effect_. And it is an effect for which the reason demands an explanation and a cause. It is a manifoldness and diversity which the logical understanding is ceaselessly endeavoring to reduce to a unity. Indeed, every movement of thought, from the first rude attempt at classification on the simple basis of resemblance, upward to the recognition of more profound ideal relations and uniform laws, until its culmination in the highest integration of reason, is but the effort of the mind to grasp the individual facts of nature in a unity of thought, and interpret the universe according to principles and ideas which the reason supplies. The moment reflective thought is directed to the phenomenal world, the questions spontaneously arise--Out of what does the phenomenal come? By what agency or efficiency does it arise? Why does it present itself in this order rather than another? Or, more specifically--What is the abiding _reality_ which sustains the array of phenomena? What is the invisible _power_ which effects all the changes we see around us? What is that unseen _presence_ which determines the forms, relations, and adaptations which every where present themselves to the reason of man? In a word, _What is that ultimate principle--the last or remotest in the order of analytic thought, the first in the order of being and of reason--which sustains and moves and organizes and governs all_--that fundamental, abiding PRIMUS which is everlastingly present behind the scenery and changes of the world--_that which always was, and now is, and ever shall be_ FIRST? Or if we permit ourselves to regard the present order of things as a necessary out-birth from the past, still we are compelled by a laborious effort of regressive thought to climb upward through a series of changes to an absolutely FIRST of the series conditioning all the other members, but itself unconditioned. Few will now claim that this is the natural and adequate cosmical conception; but, even under this mode of conception, we can not but feel that a development without a beginning of the process, a series without a first term, is impossible. "The absolute infinity of a series is a contradiction _in adjecto_. As every number, although immeasurably and inconceivably great, is impossible unless unity is given as its basis, so every series, being itself a number, is impossible unless a first term is given as its commencement." Therefore the question still returns--What is that First Principle of all things?