process of arriving at fair judgments is both laborious and painful. Instead, however, of assuming certainty because it is desirable, we would endeavor to earn it, by recognizing it as every man's duty and privilege to add to truth, in the justness, completeness, and clearness of his knowledge of it. And, since the scope of the unknown is infinite, the incitement to the fulfillment of this duty is full of hope and promise. Science, unlike dogma, does not point to fields harvested and gleaned long ago, but to continents awaiting their Columbus to pressing problems of individual, social, and political life demanding solutions by thoughtful men. And, in the fields of scientific investigation, we can see how every newly ascertained fact and law extends the horizon of Nature, adds to the area of unexplored territory, thereby stimulating the student to achievement therein. In researches respecting mind and brain, and their relations, in probing consciousness to its depths, and in the results which may follow the inquiry as to whether the intellect does or does not come into direct contact with external Nature, some of the ablest thinkers of our time place hope of more light on the chief problems of life. Our conception, then, of knowledge leads us back to the early similitude which likened it to a tree. Knowledge does not increase, like a honey-comb, cell simply added to cell, but, like an oak, whose every year of growth implies not addition merely, but vital transformation of structure. Nothing is fixed but the axis from which the branches and boughs spread out, as if they felt they had all the universe for their expansion. A stripling oak of a few seasons' growth is beautiful enough in its way; but would it be wise or useful to uproot it, shelve it in a museum, and declare it to represent a finality as to oak possibilities?
The idea of knowledge which I have sought to express makes clear the grounds whereon thought and discussion ask for full liberty. As men differing in natural ability, temperament, education, and stand-point, strive to attain views of truth, their results must inevitably vary. "Recognition of difference of view" we would, then, substitute for the offensive term "toleration of dissent," which latter phrase, from one who holds that he possesses finality, simply means the permission of known error, which he may be unwilling or unable to punish. And the differences of view which men of opposite temperaments and tendencies may entertain are often mutually completing, and become indued in a master-mind with stereoscopic relief and unity. Let me cite an example of this: Two schools of thought endeavored to explain conscience on different principles. The one held it to arise from an innate moral sense, the other from the results of experience. The philosophy of evolution includes in its explanation both series of facts from which these two schools argued. It shows how ancestral experiences of right and wrong conduct become organized in the race, and are transmitted as moral tendencies to off-
