Naturalism is not of to-day or of yesterday, but is very ancient,--as old,

indeed, as philosophy,--as old as human thought and doubt. Indeed, we may

say that it almost invariably played its part whenever man began to

reflect on the whence and the how of the actual world around him. In the

philosophical systems of Leucippus and Democritus and Epicurus it lies

fully developed before us. It persisted as a latent and silently dreaded
antagonist, even in times when "orthodox" anti-naturalistic and

super-naturalistic systems were the officially prevailing ones, and were

to all appearance generally adhered to. So in the more modern systems of

materialism and positivism, in the Systeme de la nature and in the

theory of l'homme machine, in the materialistic reactions from the

idealistic nature-speculations of Schelling and Hegel, in the discussions

of materialism in the past century, in the naturalistic writings of

Moleschott, Czolbe, Vogt, Buechner, and Haeckel, and in the still dominant

naturalistic tendency and mood which acquired new form and deep-rooted

individuality through Darwinism,--in all these we find naturalism, not

indeed originating as something new, but simply blossoming afresh with

increased strength. The antiquity of Naturalism is no reproach, and no

reason for regarding it as a matter long since settled; it rather

indicates that Naturalism is not a chance phenomenon, but an inevitable

growth. The favourite method of treating it as though it were the outcome

of modern scepticism, malice, or obduracy, is just as absurd as if the

"naturalists" were to treat the convictions of their opponents as the

result of incredible narrow-mindedness, priestly deception, senility, or

calcification of the brain-cells. And as naturalism is of ancient origin

so also do its different historical phases and forms resemble each other

in their methods, aims, and arguments, as well as in the moods,

sympathies, and antipathies which accompany them. Even in its most highly

developed form we can see that it did not spring originally from a

completed and unified principle, but was primarily criticism of and

opposition to other views.