The great result of speculation since the time of Kant is to teach us to recognize that objects are essentially related to mind, and that the principles which rule our thought enter, so to speak, into the constitution of the things we know.  A very slight acquaintance with the history even of psychology, especially in modern times, shows that facts are more and more retracted into thought.  This science, which began with a sufficiently common-sense view, not only of the reality and solidity of the things of the outer world, but of their opposition to, or independence of thought, is now thinning that world down into a mere shadow—­a something which excites sensation.  It shows that external things as we know them, and we are not concerned in any others, are, to a very great extent, the product of our thinking activities.  No one will now subscribe to the Lockian or Humean view, of images impressed by objects on mind:  the object which “impresses” has first to be made by mind, out of the results of nervous excitation.  In a word, modern psychology as well as modern metaphysics, is demonstrating more and more fully the dependence of the world, as it is known, on the nature and activity of man’s mind.  Every explanation of the world is found to be, in this sense, idealistic; and in this respect, there is no difference whatsoever between the interpretation given by science and that of poetry, or religion, or philosophy.  If we say that a thing is a “substance,” or has “a cause”; if, with the physicist, we assert the principle of the transmutation of energy, or make use of the idea of evolution with the biologist or geologist; nay, if we speak of time and space with the mathematician, we use principles of unity derived from self-consciousness, and interpret nature in terms of ourselves, just as truly as the poet or philosopher, who makes love, or reason, the constitutive element in things.  If the practical man of the world charges the poet and philosopher with living amidst phantoms, he can be answered with a “Tu quoque.”  “How easy,” said Emerson, “it is to show the materialist that he also is a phantom walking and working amid phantoms, and that he need only ask a question or two beyond his daily questions to find his solid universe proving dim and impalpable before his sense.”

“Sense,” which seems to show directly that the world is a solid reality, not dependent in any way on thought, is found not to be reliable.  All science is nothing but an appeal to thought from ordinary sensuous opinion.  It is an attempt to find the reality of things by thinking about them; and this reality, when it is found, turns out to be a law.  But laws are ideas; though, if they are true ideas, they represent not merely thoughts in the mind, but also real principles, which manifest themselves in the objects of the outer world, as well as in the thinker’s mind.