While acquaintance with the subject and heartfelt interest in it are the first essentials of convincing speech, there are other qualities that greatly strengthen discourse. First among these I would put _clearness of statement_. Jefferson declared in the Declaration of Independence that _certain_ truths are self-evident. It is a very conservative statement of an important fact; it could be made stronger: _all truth is self-evident_. The best service one can render a truth, therefore, is to state it so clearly that it can be understood. This does not mean that every self-evident truth will be immediately accepted because there are many things that interfere with the acceptance of truth.
First, let us consider depth of conviction. Some people take their convictions more seriously than others. In India I heard a missionary speak of another person as having "no opinions--nothing but convictions"; while one of the enemies of Gladstone described him as being the only person he ever knew who "could improvise the convictions of a lifetime." Depth of conviction gives great force to an individual when he is going in the right direction, but he is difficult to change if he is going in the wrong direction. When I visited the Hermitage for the first time they told me of an old coloured man, formerly a slave of Jackson's, who survived his master many years. He was, of course, an object of interest and many questions were asked in regard to Jackson's characteristics. One visitor inquired of him if he thought Andrew Jackson went to heaven. He quickly responded, "If he sot his head that way, he did."
Prejudice also delays the spread of truth. People sometimes brace themselves against arguments. If I may be pardoned a personal illustration I will cite a case of political prejudice that came under my own observation. I was speaking in a town in western Nebraska, an out-of-the-way place that I had seldom visited. A friend heard a man say, "Well, I never heard him and I thought I would come and see what he has to say." And then, with a determined look upon his face he added, "But he will not convince me." Political prejudice is not so hard to overcome as race prejudice and race prejudice is not so deep-seated as religious prejudice; but prejudice of any kind, whether it be personal, political, race, or religious, seriously interferes with the progress of truth.