Problems no less complex arise in relation to time. Looked at from the point of view of nature, no inconsistency is felt in the fact that only a short span of time is granted to the life of individuals; that they come and go in most rapid succession. For here the individuals do not rise to the consideration of anything beyond their own time; their presentation and desire are exhausted in the present; they feel no longing for a continuation of life. The position is radically changed with the entrance of thought. Thought 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: a timeless validity appertains to truth, a comprehension of things "under the form of eternity" (_sub specie aeternitatis_). To a being who, in his thought, rises to comprehension of experience from the point of view of the eternal, all temporal limitation, and especially the short duration of human life, is a source of surprise and a contradiction. The rapid sequence of generations, the perpetual decay of all that impels us so forcibly to desire life and holds us so firmly to it, seem to deprive our endeavour of all its value, and give to the whole of existence a shadowy, phantom-like character. Feelings of this kind have been aroused anew in our own time. The restlessness of the activities of our civilisation and the lack of real meaning in this civilisation, which to the present age seems to constitute the whole of life, need only to be clearly and forcibly comprehended by thought, and all its bustle and all its passion cannot prevent the emergence of an acute feeling of its dream-like nature.
The feeling of the lack of reality and depth in the life of nature will become the keener in proportion to the degree of independence thought evolves. For the more thought finds its own basis in itself, the more will it treat nature as an appearance, the more clearly will it recognise that sense, with all its obviousness and palpability, does not guarantee the possession of truth; for truth comes to us only through thought. In thought, therefore, the world of nature loses its immediacy and becomes a realm of appearances and phantoms.