But, now, what is the error of the "naturalist"? Simply that he has converted the scientific doctrine into an ontological doctrine. He really knows nothing, and cannot possibly know anything, about his atoms, except just this, that they give the law of the phenomena. He has nothing whatever to say to them in any other relation. If he proceeds, as Mr. Balfour says that he proceeds, to declare that nothing exists except atoms, that they are the ultimate realities, that they are "things in themselves," or objects independent of any subject, he is going beyond his tether, passing from science to transcendental metaphysics, and getting into hopeless confusion. In fact, after he has done his worst we may still follow Berkeley and deny the existence of matter, or declare with Clifford that atoms are only bits of mindstuff, or adopt any other metaphysical theory we please. The atoms at most are things which we judge from the analogy of the senses; and it is a pure illusion to suppose that they can ever take us into an extra-sensible world. They represent not only a convenient but an indispensable contrivance for enabling us to formulate scientific laws, such as those of light and heat; but they take us no further.