Again, in discussions on truth and duty, all men seem to agree that there is such a thing as _reason_, and that it is, more or less, to be made the umpire in settling all disputed points. It is true that very few seem to have a clear and definite idea of what this reason is, or how it is to be made an umpire. But all allow that there is such a thing, and that it has a very important office in deciding questions of truth and duty.
Then, again, among more scientific men, we hear constant reference made to our "intuitions" and our "intuitive knowledge," as if there were some fixed truths which are superior to all others. It is true, that when we come to inquire specifically as to what are these intuitions, we often find them to be acquired notions, and sometimes such as are unsupported by any evidence, or even contrary to the best kind of evidence. Nevertheless, those who use these terms all agree in the fact that there are "intuitions" and "intuitive knowledge," which are superior to any other kinds of knowledge, and involve a certainty of conviction which no reasoning can overthrow.
Then, as we advance still higher in the world of letters, we find metaphysicians and philosophers assuming that a belief in certain truths is implanted in all rational minds by the Creator as a necessary part of their constitution, and that these truths are the foundation of most of our acquired knowledge. The truths or principles of mind thus recognized are called by various names, such as _reason_, the _principles of reason_, the _primary truths_, the _intuitions_, the _intuitive truths_, the _fundamental truths_, the _principles of common sense_, the _categories_, etc.
The grand difficulty on this subject has been, that while all agree in the existence of such implanted truths, there has never been any _test_ for deciding which are these truths, in distinction from our acquired notions.
It is the object of the succeeding chapter to present the most important of these truths, and also to set forth an infallible test by which they may be distinguished from every other kind of knowledge.
And this attempt is made with a full conviction that success in such an effort is to be the foundation of that harmony of reconstruction which has been indicated as provided for the future.