There remains the question of the co-ordination of the impressions received materially by the senses. This co-ordination, for elementary sensations, is evidently identical for all beings. The snail, his horn being threatened, and man, his eye, make the same shrinking movement. Identical acts can have as cause only identical realities, or ones perceived as such. With judgment, we enter upon the mystery. If light is constant, the judgment which admits its existence is variable according to the species, and, in the higher species, according to the individual. It is clear that all eyes are affected by light, but we do not know to what degree, or according to what mode of spectral decomposition. It is the same for all other senses. Even if the reality of the sensible world be admitted, we are obliged to pronounce cautiously upon the quality of this reality, as reality perceived and judged. We then return to idealism, though having had a quite different end in view. We must retrace our steps, contemplate anew the ironic portress, and resign ourselves never to know anything save appearance. Another fact, however, remains--another fortress, perhaps, reared facing the other. This is, that matter existed before life. The gain seems slight, but it is equivalent to saying that the phenomena perceived by the senses are exterior to the senses which now perceive them; and this perhaps means that, if life becomes extinct, matter will survive life. The proposition of the idealists that the world would come to an end if there were no longer any sensibilities capable of feeling it, any intelligences capable of perceiving it, seems, therefore, untenable. And yet what would a world be, that was neither thought nor felt? We must recognize this, that when we think of a world void of thought, it still contains our thought, or it is our thought which contains it and animates it. Another phenomenon analogous to this has, perhaps, contributed much to belief in the immortality of the soul, namely, that we cannot conceive of ourselves as dead save by thinking of this death, by feeling and seeing it. The idea of our non-existence supposes, moreover, the life of our thought. That there is here an illusion due to the very functioning of the mechanism of thought is probable enough; but it is difficult not to take it into account. It would seem somewhat high-handed to make abstraction of it. We can attempt it, however, and try a new road leading "beyond thought." The way would be to consider the general movement of the things in which our thought itself is closely implicated, and by which it is rigorously conditioned. Far, perhaps, from thought thinking life, it is life that animates thought. What is anterior is a vast rhythmic undulation, of which thought is but one of the moments, one of the bounds.