The existence of substance, he then concludes, is involved in the nature of the thing itself.  Substance exists.  It does and must.  We ask, why? and we are answered, because there is nothing capable of producing it, and therefore it is self-caused; i.e. by the first definition the essence of it implies existence as part of the idea.  It is astonishing that Spinoza should not have seen that he assumes the fact that substance does exist in order to prove that it must.  If it cannot be produced and exists, then, of course, it exists in virtue of its own nature.  But supposing it does not exist, supposing it is all a delusion, the proof falls to pieces, unless we fall back on the facts of experience, on the obscure and unscientific certainty that the thing which we call the world, and the personalities which we call ourselves, are a real substantial something.  Conscious of the infirmity of his demonstration, he winds round it and round it, adding proof to proof, but never escaping the same vicious circle:  substance exists because it exists, and the ultimate experience of existence, so far from being of that clear kind which can be accepted as an axiom, is the most confused of all our sensations.  What is existence? and what is that something which we say exists?  Things—­essences—­ existences; these are but the vague names with which faculties, constructed only to deal with conditional phenomena, disguise their incapacity.  The world in the Hindoo legend rested upon the back of the tortoise.  It was a step between the world and nothingness, and served to cheat the imagination with ideas of a fictitious resting-place.

“If any one affirms,” says Spinoza, “that he has a clear, distinct—­that is to say, a true idea of substance, but that nevertheless he is uncertain whether any such substance exist, it is the same as if he were to affirm that he had a true idea, but yet was uncertain whether it was not false.  Or if he says that substance can be created, it is like saying that a false idea can become a true idea—­as absurd a thing as it is possible to conceive; and therefore the existence of substance, as well as the essence of it, must be acknowledged as an eternal verity.”

It is again the same story.  He speaks of a clear idea of substance; but he has not proved that such an idea is within the compass of the mind.  A man’s own notion that he sees clearly, is no proof that he really sees clearly; and the distinctness of a definition in itself is no evidence that it corresponds adequately with the object of it.  No doubt a man who professes to have an idea of substance as an existing thing, cannot doubt, as long as he has it, that substance so exists.  It is merely to say that as long as a man is certain of this or that fact, he has no doubt of it.  But neither his certainty nor Spinoza’s will be of any use to a man who has no such idea, and who cannot recognize the lawfulness of the method by which it is arrived at.