ALL teaching and reasoning take certain truths as granted. That the unequivocal, à priori affirmations of the reason are valid, for all the truths and principles thus affirmed, must be assumed and admitted, or every attempt to construct a science, of any kind, or to attain to certain knowledge upon any subject, is vain and even preposterous.
The sense is the power that perceives sensation and brings it within the field of consciousness. Sensation is an impression made upon the sensibility by some object without or some thought within the mind. The sense takes up, or perceives the sensation, and this perceived sensation is revealed in consciousness.
Self-consciousness also reveals to us the reason or the à priori function of the intellect. The reason is that function of the intellect which immediately beholds or intuits a class of truths which, from their nature, are not cognizable either by the understanding or the sense.
Between knowledge derived from sense and from reason there is a difference: in one case, consciousness gives us the sensation: it may be questioned whether the perceptions of the sense are a direct beholding of the object of the sensation, and consequently whether the object really exists, and is the real archetype of the sensation.
But in regard to the intuitions of the reason, this faculty directly beholds the truths which it affirms. These truths are the objects of its intuitions. They are not received at second hand.
OF THE UNDERSTANDING.
Of the imagination, and the memory, &c., I need not speak in this place.
What has been said has, I trust, prepared the way for saying that the truths of theology arrange themselves under two heads.
Every truth that must be arrived at by reasoning or induction, every truth that is attained to by other testimony than that of direct beholding, perceiving, intuiting, or cognizing, is a truth belonging to the class that needs proof.
Second. Truths of demonstration belong to the class that needs proof. When truths of demonstration are truly demonstrated by any mind, it certainly knows them to be true, and affirms that the contrary cannot possibly be true. To possess the mind of others with those truths, we must lead them through the process of demonstration. When we have done so, they cannot but see the truth demonstrated.
To the class of truths that need proof belong those of divine revelation.
All truths known to man are divinely revealed to him in some sense, but I here speak of truths revealed to man by the inspiration of the Holy Spirit.
That space and time are, and must be, that every event has and must have a cause, and such like truths, are universally known and assumed by every moral agent, whether the terms in which they are stated have ever been so much as heard by him, or not. This last is the characteristic that distinguishes first truths from others merely self-evident, of which we shall soon speak.
It is, therefore, always to be remembered that first truths are universally assumed and known, and in all our teachings, and in all our inquiries we are to take the first truths of reason for granted. It is preposterous to attempt to prove them, for the reason that we necessarily assume them as the basis and condition of all reasoning.
The mind arrives at a knowledge of these truths by directly and necessarily beholding them, upon condition of its first perceiving their logical condition.
The mind perceives, or has the notion of body. This conception necessarily developes the first truth, space is and must be.
The mind beholds or conceives of succession; and this beholding, or conception, necessarily developes the first truth, time is, and must be.
As we proceed we shall notice divers truths which belong to this class, some of which, in theory, have been denied. Nevertheless, in their practical judgments, all men have admitted them and given as high evidence of their knowing them, as they do of knowing their own existence.
Suppose, for example, that the law of causality should not be, at all times or at any time, a subject of distinct thought and attention. Suppose that the proposition in words, should never be in the mind, that "every event must have a cause," or that this proposition should be denied. Still the truth is there, in the form of absolute knowledge, a necessary assumption, an à priori affirmation, and the mind has so firm a hold of it, as to be utterly unable to overlook, or forget, or practically deny it.
First truths of reason, then, let it be distinctly remembered, are always and necessarily assumed, though they may be seldom thought of. They are universally known, before the words are understood, by which they may be expressed; and although they may never be expressed in a formal proposition, yet the mind has as certain a knowledge of them as it has of its own existence.
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, being 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 developement, and in no case could any thing else be needed, for upon the occurrence of this perception, the assumption, or developement, 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 à priori condition of all logical deduction and demonstration. Some one of these must be assumed as true, directly or indirectly, in every syllogism and in every demonstration.
In all our future investigations we shall have abundant occasion 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 estopple of all controversy.
To deny the reality of this class of truths, is to deny the validity of our most perfect knowledge. The only question to be settled is, does the truth in question belong to this class? 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.
2. The second class of truths that need no proof are self-evident truths, possessing the attributes of necessity and universality.
Of these truths, I remark--
(1.) That they, like first truths, are affirmed by the pure reason, and not by the understanding, nor the sense.
(2.) They are affirmed, like first truths, à priori; that is, they are directly beheld or intuited, and not attained to by evidence or induction.
(3.) They are truths of universal and necessary affirmation, when so stated as to be understood. By a law of the reason, all sane men must admit and affirm them, in the light of their own evidence, whenever they are understood.
This class, although self-evident, when presented to the mind, are not, like first truths, universally and necessarily known to all moral agents.
The mathematical axioms, and first principles, the à priori grounds and principles of all science, belong to this class.
(4.) They are, like first truths, universal in the sense that there is no exception to them.
(5.) They are necessary truths. That is, the reason affirms, not merely that they are, but that they must be, true; that these truths cannot but be. The abstract, the infinite, belong to this class.
To compel other minds to admit this class of truths, we need only to frame so perspicuous a statement of them as to cause them to be distinctly perceived or understood. This being done, all sound minds irresistibly affirm them, whether the heart is, or is not, honest enough to admit the conviction.
3. A third class of truths that need no proof, are truths of rational intuition, but possess not the attributes of universality and necessity.
Our own existence, personality, personal identity, &c., belong to this class.
But I must not proceed further with this statement; my design has been, not to enter too minutely into nice metaphysical distinctions, nor by any means to exhaust the subject of this lecture, but only to fix attention upon the distinctions upon which I have insisted, for the purpose of precluding all irrelevant and preposterous discussions about the validity of first and self-evident truths.
Enough, I trust, has been said to prepare your minds for the introduction of the great and fundamental axioms which lie at the foundation of all our ideas of morality and religion. Our next lecture will present the nature and attributes of moral law. We shall proceed in the light of the à priori affirmations of the reason, in postulating its nature and its attributes.