Certainly no one can be happy if he does not have what he wants. The seeker for truth professes to want truth. The skeptic, therefore, cannot be happy; he cannot accomplish the aim of his life. Nor can his useless search provide any guidance for day-to-day living. The skeptics wish to act on what is probable; but if “probable” means only what seems good to a person at the moment, a man might commit the worst crime without blame, provided he thought it was probably good. But probability may mean something more. It may mean “approximating the truth.” The skeptics call propositions false, doubtful, probable, and plausible. Their basic principle, however, does not in consistency permit them to use any of these terms. A false proposition is one opposite to the truth. How then can one say that a proposition is false, unless one knows the truth? A doubtful proposition is one that might possibly be true; a probable or plausible proposition resembles or approximates the truth. But it is impossible to apply these terms without knowing the truth by which they are determined. One might well ask, Is it true that a foredoomed search for truth is wisdom? The skeptic would have to reply that he did not know. Is it probable that such a search is wisdom? Or with respect to everyday living, is it probable or doubtful that eating lunch today is wise? Again the skeptic could not know. A theory of probability must itself be based on truth, for if the method of determining the probable wisdom of eating lunch is false, the conclusion that it is safe to eat lunch could not be known to be probable. Without the possession of the truth, therefore, it is impossible to act rationally even in the most ordinary situations.
Now, fortunately, truth is not only possible to attain, it is impossible to miss. There are some truths indubitably certain. Even sensation is not uniformly deceptive, and, more to the point, thought is not altogether dependent on sensation. For example, complete disjunctions, such as, either you are awake or asleep, and implications based on them, such as, if there are only four elements, there are not five, are unquestionably true. Similarly, the law of contradiction, which underlies all logical forms, cannot be disputed; and at this point it might be well to review Aristotle’s pertinent remarks. Furthermore, the propositions of mathematics cannot be doubted; nor is this science any more than logic based on sensory experience. Even if it were possible to sense a given number, such as three, ratios, divisions, and the other operations cannot be perceived. Things perceived by sense, rivers and trees, do not long endure; but that the sum of three and seven is ten endures forever. There never was a time when three and seven did not add up to ten, nor will there ever be a time. Such inviolable, eternal truths cannot be abstracted from a mutable matric. Nor can the given numbers themselves be so abstracted. Three – or, better, one, since the number series depends on one – cannot be perceived by sense, for every object of sensation is many, not one. Bodies have parts innumerable; at least they have three dimensions, a center and a surface, a right and left side; and therefore no body can be one. If, therefore, unity pure and simple is not an attribute of body, unity cannot be abstracted from body; for we cannot abstract what is not there. The truths of mathematics, accordingly, are grasped, not by sense, but by reason or intellectual intuition. And these truths are indubitable. But the most crushing refutation of skepticism comes when Augustine asks his opponent, Do you know that you exist? If he so much as hears the question, there can be no doubt about the answer. No one can be in doubt as to his own existence. “We both have a being, know it, and love both our being and knowledge. And in these three no false appearance can ever deceive us. For we do not discern them as things visible, by sense…. I fear not the Academic arguments on these truths that say, ‘What if you err?’ If I err, I am. For he that has no being cannot err, and therefore my error proves my being.” Thus in the immediate certainty of self-consciousness a thinker has contact with being, life, mind, and truth.
Twelve hundred years later Descartes repeated the argument, Cogito, ergo sum; only Descartes, in order to appear original, altered its form and spoiled its force. Further, Descartes made this proposition the premise from which all other truths were to be derived. Augustine indeed derived many other truths, possibly too man, from this original certainty, but it was not the only original certainty. It is one case, a particularly obvious case, of intellectual intuition.Self-knowledge is an epistemic necessity. It is an intellectual intuition, a concept which Clark elsewhere equates with "innate ideas" (Ibid., pgs. 127-128) or "indubitable truths" which "the human mind as such necessarily possesses" (pgs. 182-184). All of this falls in quite nicely with the argument that self-knowledge is a necessary yet insufficient condition for knowledge.
Clark also grappled with the "immensely difficult" subject of self-knowledge in his commentary on 1 John. Note his resolution to it:
Here is the difficulty Hodge does not face. How can one know that his assurance is not a delusion?
But where there is true faith, the want of assurance is to be referred either to the weakness of faith or to erroneous views of the plan of salvation. Many sincere believers are too introspective. They look too exclusively within, so that their hope is graduated by the degree of evidence of regeneration which they find in their own experience…. We may examine our hearts with all the microscopic care prescribed by President Edwards…. And never be satisfied that we have eliminated every ground of misgiving and doubt.Hodge continues by listing five grounds of assurance – external, not internal grounds. But the reader must judge for himself whether or not Hodge has eliminated every ground of misgiving and doubt. In fact, while Hodge’s external grounds are exceedingly important, and usually underemphasized, ignored, or even explicitly denied in contemporary pietism, our text in John’s Epistle certainly seems to depend on internal factors and our mental ability to arrive at a correct psychological analysis of them. Does regeneration guarantee competence in psychology? It must be admitted, therefore, that these apparently simple verses are in truth immensely difficult. (First John, 1980, pg. 107)
With some diffidence and reserve because of the complex difficulties, I suggest the following: By loving in deed and truth we shall know that we are of the truth. (Ibid., pg. 113)
Assurance of eternal life can be deduced from a knowledge that one is a believer. Of course, as the negro spiritual says, “Everybody talking about heaven ain’t going there.” With constant frequency people are assured of many things untrue. Indeed certainty increases in direct proportion to ignorance. The less educated a man is, the more things of which he is certain. If this obvious truth disturbs anyone, he should also realize that assurance is not essential to salvation. Different people have different mentalities. John Bunyan was so morbid he could hardly have had much assurance. With others more careless, doubts never arise. But if one knows, if one has a clear intellectual understanding that he believes, he should have legitimate assurance. (Ibid., pg. 161)So not only is self-knowledge an intellectual necessity, it is a practical necessity. Here Clark argues - as I have - that self-knowledge is necessary for assurance of salvation. Assurance is a deduction, and as a theorem deduced is only as certain as the premise from which it is deduced, a knowledge or clear intellectual understanding of one's belief is requisite in order to function as legitimate grounds for assurance.