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THE POPULAR SCIENCE MONTHLY.

so many others which have served as pillars of imposing metaphysical structures, is the precise opposite of the truth. All material reality is, in its nature, not absolute, but essentially relative. All material reality depends upon determination; and determination is essentially limitation, as even Spinoza well knew. A "thing in and by itself" is an impossibility. And I may add here (without dwelling upon it further, a discussion of this subject being foreign to my theme), the "thing per se" is not only impossible, according to the criteria of our intellect, but it is not the object of knowledge, in any sense, and cannot, therefore, be the legitimate subject of speculation. As Ferrier would say, we can neither know it nor be ignorant of it. I do not speak here merely of objects without relation to the intellect, in the sense of Ferrier's "Theory of Ignorance," but of objects without relation to each other. "We only know anything," justly says John Stuart Mill ("Examination of Sir W. Hamilton's Philosophy," i., 14), "by knowing it as distinguished from something else; all consciousness is of difference; two objects is the smallest number required to constitute consciousness; a thing is only seen to be what it is by contrast with what it is not." Here, again, the doctrines of psychology are corroborated by the teachings of the science of language. "Words," says Rev. Richard Garnett ("Philological Essays," p. 282), "express the relations of things; and this, it is believed, is strictly applicable to every word in every language, and under every possible modification."

Among those who have had occasion of late to insist upon the relativity of all objective reality is Prof. Helmholtz. Speaking of the inveterate prejudice according to which the qualities of things must be analogous to, or identical with, our perceptions of them, he says ("Die neueren Fortschritte in der Theorie des Sehens," Pop. wiss. Vortraege II., 55, et seq.): "Every property or quality of a thing is in reality nothing else than its capability of producing certain effects on other things. The effect occurs either between connatural parts of the same body, so as to produce differences of aggregation, or it proceeds from one body to another, as in the case of chemical reactions; or the effects are upon our organs of sense and manifest themselves as sensations such as those with which we are here concerned (the sensations of sight). Such an effect we call a 'property,' its reagent being understood without being expressly mentioned. Thus we speak of the 'solubility' of a substance, meaning its behavior toward water; we speak of its 'weight,' meaning its attraction to the earth; and we may justly call a substance 'blue,' under the tacit assumption that we are only speaking of its action upon a normal eye. But, if what we call a property always implies a relation between two things, then a property or quality can never depend upon the nature of one agent alone, but exists only in relation to and dependence on the nature of some second object acted upon. Hence, there is really no sense in talking of properties of light which belong to it absolutely, indepen-