In admitting that sensations are comparable in this sense, that two odors, for instance, regarded as of the same kind, can be compared with each other in the same way as either can be compared with a sound or a taste, Bergson evidently means that they can be distinguished as different; and he regards this as implying that sensations are absolutely heterogeneous with each other, _absolutely_ different. This phrase, I am sure, conceals a bald contradiction. It seems to mean a relation, namely difference, in which, however, the terms are absolute, that is not in relation. Difference cannot be so conceived. Difference, I submit, cannot be conceived without that (_common to the differing terms_) in respect of which they are different. Monsieur Bergson, therefore, in admitting that sensations are comparable in any sense, is still confronted with an element common to all sensations; he has still to eliminate the character of homogeneity from sensation, by virtue of which a purely subjective evaluation of their relative intensities is possible. The root of the difficulty Monsieur Lévy-Bruhl has shown[105] to be a reific separation of quantity and quality, which are separable in truth only by abstraction of attention. Real existence in absolute homogeneity or space, as Bergson represents the existence of the external world, is as unthinkable as real existence in absolute heterogeneity, which existence is consciousness or life, for Bergson. External things, he says, which do not lapse (“_ne durent pas_”), seem to us, nevertheless, to lapse like us because to each instant of our lapsing duration a new collective whole of those simultaneities which we call the universe corresponds. “Does this not imply,” writes Lévy-Bruhl, “a preestablished harmony much more difficult to accept than that of Leibniz? Leibniz supposes a purely ideal concord between forces of the same nature. Monsieur Bergson asks us to admit an indefinite series of coincidences, for each instant, between ‘a real duration, whose heterogeneous moments compenetrate,’ and a space which, not lapsing, has no moments at all. Monsieur Bergson really places external reality, which does not lapse, in a sort of eternity. He ingeniously shows that everything in space may be treated as quantity and submitted to mathematics. Now, mathematical verities, expressing only relations between given magnitudes, are abstracted from real lapsing duration. All the laws reduce to analytical formulæ. But then they are, according to the saying of Bossuet, eternal verities, and how shall the real be distinguished from the possible?”