So, also, all the doctrines and duties, both of natural and revealed religion, can be shown to rest on these intuitive truths. This indicates the propriety of the name given to these first principles as _principles of reason_ and _fundamental truths_. Here, then, is presented the foundation of the hope so confidently expressed, that a time is coming when, in all the great questions which now agitate humanity with doubts, discussions, and conflict, there shall result universal harmony and unity of opinion. If such intuitive principles are implanted in all human minds; if there is a _certain test_ by which these principles can be eliminated and established; and if, by a sure process of reasoning, every correct practical and religious opinion can be shown to rest on these principles, and every false one to contradict them, then we can plainly perceive the true path to this golden age. It is to cultivate the powers of the human intellect, to train every mind, from early life, to detect the true laws of reason, and to practice accurately the process of reasoning. Not that this alone will suffice without the attending cultivation of the moral powers, and the promised blessing of heavenly aid. But the first would powerfully tend to secure the second, and then the third would inevitably be bestowed. Before proceeding farther, it is desirable to recognize the fact that the word _reason_ is used in several ways. Sometimes it signifies simply the intuitive truths. Sometimes it includes all those principles and powers of mind which are employed in the act of reasoning. Sometimes it refers to the intellect in distinction from the feelings. In all cases, however, the connection will determine in which of these uses it is employed. [1] Note A. CHAPTER III. SOURCES OF HUMAN KNOWLEDGE. We have seen that there are certain intuitive truths, the belief of which is implanted as a part of our mental constitution, and that there is a _test_ by which we can distinguish them from all other kinds of knowledge. We have seen, also, that we are dependent on these truths for a large portion of our acquired knowledge, inasmuch as they are the basis of _reasoning_, which is that process by which we gain new truths by the aid of those already believed. It has been intimated, also, that it is chiefly by the aid of these principles that a harmonious system of truth is to be anticipated, in which all minds will eventually agree, at least in all great questions involving the eternal interests of our race. We will now proceed in an inquiry as to what are _the sources of human knowledge_ in addition to these first implanted truths.