Substantial truth means the truth which we see—the inward sight, the radical experience. Formal truth is the verbal statement, and consists in accuracy of expression. And so of error. Substantial error means error in regard to the substance, and is necessarily inadequacy of inward experience. Strictly speaking, there cannot be substantial error; for error, in regard to the substance of truth, is purely negative. It is not-seeing. It is failing to perceive the truth, either from want of opportunity, weakness of vision, or neglect in looking. But formal error is not merely defect: it may also be mistake. We may misstate the truth, and say what is radically false. From this source come contradictions; and, where two statements are contradictory, both cannot be true. Falsehood, therefore, originates with the statement. The errors of insight are merely defects; but the errors of statement may be positive falsehoods. This leads us to take a special view of theological controversies. In all great controversies, in the conflicts of ages, where the good and wise have stood opposed to each other, century after century, it is probable that there are truth and error on both sides. Each side may hold some truth which the other has not seen. There is, therefore, also substantial error on both sides; for each may have failed to see some phase of truth which the other has recognized. But there may be formal error, or error of statement, even where there is substantial truth; for the truth may be overstated, or understated, or misstated, and a false expression given to a true observation. What, then, is the duty of those who stand opposed to each other in these controversies—of Catholics and Protestants, Christians and Deists, Orthodox and Unitarians? They have plainly a twofold duty to themselves as well as to their opponents. They ought to increase their insight, and to improve their statements; to deepen and widen their hold of the substance; to correct and improve their expression of the form. The first is the work of religion; the second, that of theology. The first is infinitely the most important, because the life of the soul depends on the sight of truth. This is its food, without which it will starve and die. But it is also important that it should improve its theology, because a correct theology is a help to insight, and a ground of mental communion. § 11. The Orthodox and Liberal Parties in New England.