Our investigations of history leads us, too, to differentiate between the temporary and the eternal in the realm of thought. We find at a certain period of history a trend of thought that can largely be accounted for by the special conditions of life at the time, and which disappears at a later age. But in addition to this we become aware of truths that have found a place in the thoughts of various ages and countries, and we are led to regard these as the eternal truths--expressions of an eternal ever-present reality. This eternal present we find to be something independent of time, something that breaks the barriers between the past, present, and future. "Thought," says Eucken, "does not drift along with time; as certainly as it strives to attain truth it must rise above time, and its treatment must be timeless." The beliefs of any age are too much coloured by the special circumstances of that age to express the whole of truth, yet beneath the beliefs of the ages there is often an underlying truth, and this underlying truth is the eternal truth, which is not affected by time, and at the basis of which is the eternal reality. This eternal truth persisting through a variety of temporary and more or less correct expressions of it is to be observed in a marked manner in the moral ideas of mankind. What a variety of ethical doctrines have been expounded and believed, yet how striking the similarity that becomes apparent when they are further examined! In practice, the standard of morality has often been based on mere utility, but it has taken a higher and more absolute basis in the mind of man. Ideas concerning morality have generally been nobler than can be accounted for by environment, and by the subjective life of the individual. Why this ultimate consistency in the moral aspirations of the ages, why a categorical imperative, and why does conscience exist in the human being?--these facts cannot be accounted for if there is no deeper basis for life than the life of humanity at any definite period of time. The unchangeable laws of logic, too, are instances of the eternal truth. The principles of the validity of thought are entirely independent of individuals, of the passage of time, and of the environment of man. "Our thought cannot advance in the definite work of building up science without producing and employing a definite logical structure, with fixed principles; these principles are immanent in the work of thought, they are above all the caprice and all the differences of the individuals." Whence again this consistency in a changeable and subjective world?