90. Science considered subjectively, is a certain and evident cognition of truths deduced from certain principles by means of demonstration; considered objectively, it is a complete system of demonstrated truths deduced from the same common principles. -- considered as existing in the intellect, that is, subjectively, must be certain cognition, otherwise it would not be perfect; it must be evident cognition, otherwise it would not account to the fund for the subordinate truths deduced from the principles. Finally, it must be cognition of the truths deduced from certain principles, for the conclusions cannot be stronger than the premises. Science considered objectively, is a body of co-ordinated truths deduced from the same principles and constituting what is called a scientific system. It is in this latter sense that the word science is usually understood.
91. A science must be both one and multiple; one in respect to the same set of principles whence flow the truths embraced under the science; multiple in respect to the deductions made from the principles. -- Those principles from which the mind deduces the truths contained therein, are, as it were, the foundations of the science and constitute its unity. This unity is formal and not material; for, though a science treats of objects materially multiple, yet these objects are considered under an aspect by which they are referred to one and the same set of principles, and hence the science is one.
92. Every science is specified by its object. -- The formal object of a science constitutes its unity and makes it this or that science; hence the sciences are distinguished from one another by the diversity of their formal objects. Thus, a science is natural or supernatural according as its object is natural or supernatural truth; it is speculative or practical according as its object is purely theoretical truth or a truth the knowledge of which may serve as a rule of action.
Two sciences are said to be distinct when the object of one has certain relations to that of the other, as, "Geometry and Astronomy." They are said to be separate when their objects have no relation to each other, as, "Algebra and Morals."
93. Philosophy is the science that governs all the other sciences, which may, therefore, be divided and classified according to the divisions instituted in philosophy. -- Philosophy is the fundamental science and ranks next to Sacred Theology; for it treats of being in itself and in general. But as every other science treats of being under some particular aspect, it follows that each has its foundation in philosophy, and from it derives its first principles.
The division of philosophy furnishes the basis for the general division of the other sciences, whose dignity and classification should be established according the greater or less degree of abstraction of their object from matter. Thus, to real philosophy or metaphysics the physical or natural sciences and mathematics are related; to rational philosophy the philological sciences; to moral philosophy, jurisprudence, aesthetics, and the political sciences.
But if philosophy may justly claim superiority over all other human sciences, it is itself surpassed by the divine science of theology, which is as far above philosophy as the divine intelligence is above human reason.