That men should keep their compacts is certainly a great and undeniable rule in morality. But yet, if a Christian, who has the view of happiness and misery in another life, be asked why a man must keep his word, he will give this as a reason:-- Because God, who has the power of eternal life and death, requires it of us. But if a Hobbist be asked why? he will answer:-- Because the public requires it, and the Leviathan will punish you if you do not. And if one of the old philosophers had been asked, he would have answered:-- Because it was dishonest, below the dignity of a man, and opposite to virtue, the highest perfection of human nature, to do otherwise.

In my opinion, the Christian in this passage is expressing a moral point of view, the Hobbist speaks from a legal perspective, and the old philosopher is being ethical.

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The epistemological question -- What is truth? -- is no doubt as old as the faculty of human reason. It is a question with which mankind will forever contend. Locke addressed this question, and in my opinion he gave a better answer than most.

Here is some material excerpted from one of his lesser known works, Some Observations on the Conduct of the Understanding in the Pursuit of Truth. It was first published in 1762, almost sixty years after his death. In this essay Locke deals not so much with the question of what truth is, but with the way we ought to employ our minds when we seek it.

Let not men therefore, that would have a sight of what every one pretends to be desirous to have a sight of -- truth in its full extent -- narrow and blind their own prospect. Let not men think there is no truth but in the sciences that they study, or books that they read. To prejudge other men's notions, before we have looked into them, is not to show their darkness, but to put out our own eyes. "Try all things, hold fast that which is good," is a divine rule, coming from the Father of light and truth, and it is hard to know what other way men may come at truth, to lay hold of it, if they do not dig and search for it as for gold and hid treasure; but he that does so must have much earth and rubbish before he gets the pure metal; sand and pebbles and dross usually lie blended with it, but the gold is nevertheless gold, and will enrich the man that employs his pains to seek and separate it. Neither is there any danger he should be deceived by the mixture. Every man carries about him a touchstone, if he will make use of it, to distinguish substantial gold from superficial glitterings, truth from appearances. And, indeed, the use and benefit of this touchstone, which is natural reason, is spoiled and lost only by assuming prejudices, overweening presumption, and narrowing our minds. The want of exercising it in the full extent of things intelligible, is that which weakens and extinguishes this noble faculty in us.

Every one is forward to complain of the prejudices that mislead other men or parties, as if he were free and had none of his own. This being objected on all sides, it is agreed that it is a fault and a hindrance to knowledge. What now is the cure? ... The only way to remove this great cause of ignorance and error out of the world is, for every one impartially to examine himself. If others will not deal fairly with their own minds, does that make my errors truths? or ought it to make me in love with them and willing to impose on myself? ... Every one declares against blindness, and yet who almost is not fond of that which dims his sight, and keeps the clear light out of his mind, which should lead him into truth and knowledge? False or doubtful positions, relied upon as unquestionable maxims, keep those in the dark who build on them. Such are usually the prejudices imbibed from education, party, reverence, fashion, interest, &c. This is the mote that every one sees in his brother's eye, but never regards the beam in his own. For who is there almost that is ever brought fairly to examine his own principles, and see whether they are such as will bear the trial? But yet this should be one of the first things every one should set about, and be scrupulous in, who would rightly conduct his understanding in the search of truth and knowledge.

Truth is all simple, all pure, will bear no mixture of anything else with it. It is rigid and inflexible to any bye-interests, and so should the understanding be, whose use and excellency lie in conforming itself to it. To think of everything just as it is in itself, is the proper business of the understanding, though it be not that which men always employ it to. ... Nobody will be at such an open defiance with common sense, as to profess that we should not endeavour to know and think of things as they are in themselves, and yet there is nothing more frequent than to do the contrary; and men are apt to excuse themselves, and think they have reason to do so, if they have a pretence that it is for God, or a good cause ... But God requires not men to wrong or misuse their faculties for him, nor to lie to others or themselves for his sake ... And as for a good cause, that needs not such ill helps; if it be good, truth will support it, and it has no need of fallacy or falsehood.

Truth, whether in or out of fashion, is the measure of knowledge and the business of the understanding; whatsoever is besides that, however authorised by consent or recommended by rarity, is nothing but ignorance or something worse.

Those who have read of everything are thought to understand everything too, but it is not always so. Reading furnishes the mind only with materials of knowledge; it is thinking makes what we read ours. We are of the ruminating kind, and it is not enough to cram ourselves with a great load of collections; unless we chew them over again they will not give us strength and nourishment. There are indeed in some writers visible instances of deep thoughts, close and acute reasoning, and ideas well pursued. The light these would give would be of great use if their reader would observe and imitate them; all the rest at best are but particulars fit to be turned into knowledge, but that can be done only by our own meditation and examining the reach, force, and coherence of what is said ... For all that is to be found in books is not built upon true foundations, nor always rightly deduced from the principles it is pretended to be built on.

There is not seldom to be found ... those ... who with an unwearied industry employ their whole time in books, who scarcely allow themselves time to eat or sleep, but read, and read, and read on, yet make no great advances in real knowledge, though there be no defect in their intellectual faculties to which their little progress can be imputed. The mistake here is, that it is usually supposed that by reading, the author's knowledge is transfused into the reader's understanding; and so it is, but not by bare reading, but by reading and understanding what he wrote. Whereby I mean ... to see and follow the train of his reasonings, observe the strength and clearness of their connexion, and examine upon what they bottom. ... so much as he sees of this connexion, so much he knows of the truth or probability of that author's opinions.

He that rides post through a country may be able from the transient view to tell how in general the parts lie, and may be able to give some loose description of here a mountain and there a plain, here a morass and there a river, woodland in one part and savannah in another. Such superficial ideas and observations as these he may collect in galloping over it; but the more useful observations of the soil, plants, animals, and inhabitants, with their several sorts and properties, must necessarily escape him; and it is seldom men ever discover the rich mines without some digging. Nature commonly lodges her treasure and jewels in rocky ground. If the matter be knotty and the sense lies deep, the mind must stop and buckle to it, and stick upon it with labour and thought and close contemplation, and not leave it until it has mastered the difficulty and got possession of truth. But here care must be taken to avoid the other extreme; a man must not stick at every useless nicety, and expect mysteries of science in every trivial question or scruple that he may raise. He that will stand to pick up and examine every pebble that comes in his way, is as unlikely to return enriched and laden with jewels, as the other that travelled full speed. Truths are not the better or the worse for their obviousness or difficulty, but their value is to be measured by their usefulness and tendency. Insignificant observations should not take up any of our minutes, and those that enlarge our view and give light towards further and useful discoveries, should not be neglected, though they stop our course and spend some of our time in a fixed attention.

... we should keep a perfect indifferency for all opinions, not wish any of them true, or try to make them appear so, but being indifferent, receive and embrace them according as evidence, and that alone, gives the attestation of truth. ... They that do not keep up this indifferency in themselves for all but truth, not supposed, but evidenced in themselves, put coloured spectacles before their eyes, and look at things through false glasses, and then think themselves excused in following the false appearances which they themselves put upon them.

There are fundamental truths that lie at the bottom, the basis upon which a great many others rest, and in which they have their consistency. These are teeming truths, rich in store, with which they furnish the mind, and, like the lights of heaven, are not only beautiful and entertaining in themselves, but give light and evidence to other things, that without them could not be seen or known. Such is that admirable discovery of Mr. Newton, that all bodies gravitate to one another, which may be counted as the basis of natural philosophy ... Our Saviour's great rule, that "we should love our neighbour as ourselves," is such a fundamental truth for the regulating human society, that I think by that alone one might without difficulty determine all the cases and doubts in social morality. These and such as these are the truths we should endeavour to find out, and store our minds with.