Thus, it should be distinctly said, the first-truths of reason lie so deep in the mind as perhaps seldom to appear directly on the field of conscious thought, and yet so absolutely does the mind know them that it can no more forget, overlook, or practically deny them, than it can forget, overlook, or in practice deny its own existence.

I have said that all reasoning proceeds upon the assumption of these truths. It must do so of necessity. It is preposterous to attempt to prove first-truths to a moral agent:

for if a moral agent, he must absolutely know them already, and if he did not, in no possible way could he be put in possession of them except by presenting to his perception the chronological condition of their development, and in no case could any thing else be needed, for upon the occurrence of this perception, the assumption or development follows by a law of absolute and universal necessity. And until these truths are actually developed, no being can be a moral agent.

There is no reasoning with one who calls in question the first-truths of reason, and demands proof of them. All reasoning must, from the nature of mind and the laws of reasoning, assume the first-truths of reason as certain, and admitted, and as the a priori condition of all logical deductions and demonstrations. Some one of these must be assumed as true, directly or indirectly, in every syllogism and in every demonstration.

In all our future investigations in the line of truth we shall pursue, we shall have abundant occasions for the application and illustration of what has now been said of first-truths of reason. If, at any stage of our progress, we light upon a truth of this class, let it be borne in mind that the nature of the truth is the preclusion, or as lawyers would express it, the estoppel of all controversy.

To deny the reality of this class of truths is to deny the validity of our most perfect knowledge and of course it is a denial of the validity of our faculties. The only question to be settled in respect to this class of truths, is, does the truth in question belong to this class? There are many of this class that have not been generally recognized as belonging to it. Of this we shall have abundant instances fall in our way as we proceed in our investigations. There are many truths which men, all sane men, certainly know, of which they not only seldom think, but which, in theory, they strenuously deny.

Before I dismiss this branch of our subject, I will mention some of the many truths that undeniably belong to this class, leaving others to be mentioned as we proceed and fall in with them in future investigations.

I have already noticed three of this class, to wit; the truth of causality the existence of space and of time. That the whole of any thing is equal to all its parts, is also a truth of this class, universally and necessarily known and assumed by every moral agent. Also, that a thing cannot be and not be at the same time.

A third class of self-evident truths are particular truths of reason. The reason directly intuits and affirms them. They are truths of certain knowledge, but have not the attributes of universality or infinity. To this class belong the truths of our own existence, of personal identity, and individuality. These are not truths of sensation, nor are they first or self-evident truths according to the common use of those terms. Yet they are truths of rational intuition, and are seen to be true in the light of their own evidence, and as such are given to us as undoubtable verities by consciousness.

All the truths that come within the pale of our own experience, that is, all our mental exercises and states are truths self-evident to us. We need no proof of them. Whether they are phenomena or states of the Intellect, of the Will, or of the Sensibility. When thus spoken of, in mass, they cannot be called self-evident truths except in the sense that to ourselves they appear on the field of consciousness as facts or realities, and we know or affirm them with undoubting certainty.

Truths of sensation, I have said, are in a certain sense self-evident truths. That is, they are facts of which the mind has direct knowledge through the medium of the senses. In speaking of truths of sensation as in some sense self-evident, I mean of course truths or facts of our own senses, or those revealed directly to us by our senses. I know it is not common to speak of this class of truths as self-evident; and they are not so in the sense in which simple rational intuitions are. Yet they are facts or truths which need no proof to establish them to us. The fact that I hold this pen in my hand is as really self-evident to me as that three and two are five. I as really know or perceive the one as the other, and neither the one nor the other needs any proof. It is not my design to exhaust this subject, nor to enter upon nice and highly metaphysical distinctions, but only to give hints and make suggestions that will call your attention to the subject, and meet our necessities during our present course of study, leaving it to your convenience to enter upon a more critical analysis of this subject.

Of truths that require proof, the first class to which I must call attention is the truths of demonstration. This class of truths admit of so high a degree of proof that when the demonstration is complete, the intelligence affirms that it is impossible that they should not be true. This class when truly demonstrated, are known to be true with no less certainty than self-evident truths: but the mind arrives not at the perception and knowledge of them in the same way. That class is arrived at universally, directly and a priori, that is, by direct intuition without reasoning. This class is arrived at universally by reasoning. The former are obtained without any logical processes, while this last class is always and necessarily obtained as a result of a logical process. We often get these truths by a process strictly logical without being at all aware of the way in which we came to be possessed of them. This class, then, unlike the other, are not to be communicated and established without reasoning, but by reasoning. In this class of truths the mind from its own laws will not rest unless they be demonstrated. They admit of demonstration, and from their nature and the nature of the intelligence, they must be demonstrated before they can be known and rested in as certain knowledge. Many of them may be received in the sense of being believed without an absolute demonstration. But the mind cannot properly be said to know them until it has gone through with the demonstration, and then it cannot but know them.

To possess the mind of a first-truth of reason you need only to present the chronological condition of its development. To reveal a self-evident truth of reason, you need only to state it in terms of sufficient perspicuity. But to prove a truth belonging to the class now under consideration you must fulfill the logical conditions of the intellect's affirming it. That is, you must demonstrate it.

The next class to be considered are truths of revelation. I mean truths revealed by divine Inspiration. All truths are in some way revealed to the mind, but not all by the Inspiration of the Holy Spirit. Some of this class are known and some only believed by the mind. That is, some of these truths are objects or truths of knowledge or of intuition when brought by the Holy Spirit within the field of vision or intuition. Others of them are only truths of faith or truths to be believed. The divinity of the Lord Jesus Christ is a truth of revelation of the first class, that is, a truth of intuition or of certain knowledge when revealed to the mind by the Holy Spirit. This truth, when thus revealed, the pure reason directly intuits. It knows that Jesus is the true God and eternal life by the same law by which it knows the first-truths of reason. The only account the soul can give of this truth is, that it knows it to be true. It sees or perceives it to be true. But this perception or intuition is conditionated upon the revelation of the Holy Spirit. "He shall take of mine," said Jesus, "and shew it unto you." More on this topic in its proper place. The facts and truths connected with the humanity of the Lord Jesus are of the second class of truths of revelation, that is, they are only truths of belief or of faith, as distinct from truths of the pure reason or of intuition.

This class of truths, from their nature, are not susceptible of intuition. They may be so revealed that the soul will have no doubt of them, and hardly distinguish them from truths of certain knowledge; nevertheless, they are only believed and not certainly known as truths of intuition are.

The Bible is not of itself, strictly and properly a revelation to man. It is, properly speaking, rather a history of revelations formerly made to certain men. To be a revelation to us, its truths must be brought by the Holy Spirit within the field of spiritual vision. This is the condition of our either knowing or properly believing the truths of revelation. `No man can say that Jesus is the Lord, but by the Holy Spirit.' `No man can come to me, except the Father which hath sent me, draw him.' `They shall all be taught of God.' `The natural man receiveth not the things of the Spirit of God, neither can he know them, because they are spiritually discerned.' `He that is spiritual [has the Spirit,] judgeth all things.'

But I must not in this place dwell longer upon this subject. I would only add now that those who call in question the divinity of Christ exhibit conclusive evidence that Christ has never been revealed to them by the Holy Spirit. Those who hold his divinity as a theory or opinion are not at all benefitted by it, for Christ is not savingly known to any except by the revelation of the Holy Spirit.

To the classes of truths already considered might be added several others, such as Probable Truths, Possible Truths, etc.