So far as Professor Haeckel's writings are read by the thoroughly educated and well-informed, they can do nothing but good. They may not, indeed, convey anything particularly new, but they furnish an interesting study in scientific history and mental development. So far, however, as they are read by unbalanced and uncultured persons, with no sense of proportion and but little critical faculty, they may do harm, unless accompanied by a suitable qualification or antidote, especially an antidote against the bigotry of their somewhat hasty and scornful destructive portions.
To the intelligent artisan or other hard-headed reader who considers that Christian faith is undermined, and the whole religious edifice upset, by the scientific philosophy advocated by Professor Haeckel under the name "Monism," I would say, paraphrasing a sentence of Mr Ruskin's in a preface to Sesame and Lilies:—Do not think it likely that you hold in your hands a treatise in which the ultimate and final verity of the universe is at length beautifully proclaimed, and in which pure truth has been sifted from the errors of all preceding ages. Do not think it, friend: it is not so.
For what is this same "Monism?"
Professor Haeckel writes almost as if it were a recent invention, but in truth there have been many versions of it, and in one form or another the idea is quite old, older than Plato, as old as Parmenides.
The name "Monism" should apply to any philosophic system which assumes and attempts to formulate the essential simplicity and oneness of all the apparent diversity of sensual impression and consciousness, any system which seeks to exhibit all the complexities of existence, both material and mental—the whole of phenomena, both objective and subjective—as modes of manifestation of one fundamental reality.
According to the assumed nature of that reality, different brands of monistic theory exist:—
1. There is the hypothesis that everything is an aspect of some unknown absolute Reality, which itself, in its real nature, is far beyond our apprehension or conception. And within the broad area thus suggested may be grouped such utterly different universe-conceptions as that of Herbert Spencer and that of Spinoza.
2. According to another system the fundamental reality is psychical, is consciousness, let us say, or mind; and the material world has only the reality appropriate to a consistent set of ideas. Here we find again several varieties, ranging from Bishop Berkeley and presumably Hegel, on the one hand, to William James—who, in so far as he is a monist at all, may I suppose be called an empirical idealist—and solipsists such as Mach and Karl Pearson, on the other.
3. A third system, or group of systems, has been in vogue among some physicists of an earlier day, and among some biologists now; viz., that mind, thought, consciousness are all by-products, phantasmagoria, epiphenomena, developments and decorations, as it were, of the one fundamental all-embracing reality, which some may call "matter," some "energy," and some "substance." In this category we find Tyndall—at any rate the Tyndall of "the Belfast address"—and here consistently do we find Haeckel, together with several other biologists.
This last system of Monism, though not now in favour with philosophers, is the most militant variety of all; and accordingly it has in some quarters managed to obtain, and it certainly seems anxious to obtain, a monopoly of the name.