188. Such a doctrine could not help being at once confused in its account of reality, and insecure in its doctrine alike of the human spirit and of God. On the recognition of relations as constituting the _nature_ of ideas rests the possibility of any tenable theory of their reality. An isolated idea could be neither real nor unreal. Apart from a definite order of relation we may suppose (if we like) that it would _be_, but it would certainly not be real; and as little could it be unreal, since unreality can only result from the confusion in our consciousness of one order of relation with another. It is diversity of relations that distinguishes, for instance, these letters as they now appear on paper from the same as I imagine them with my eyes shut, giving each sort its own reality: just as upon confusion with the other each alike becomes unreal. Thus, though with Locke simple ideas are necessarily real, we soon find that even according to him they are not truly so in their simplicity, but only as related to an external thing producing them. He is right enough, however inconsistent with himself, in making relation constitute reality; wrong in limiting this prerogative to the one relation of externality. When he afterwards, in virtual contradiction to this limitation, finds the reality of moral and mathematical ideas just in that sole relation to the mind, as its products, which he had previously made the source of all unreality, he forces upon us the explanation which he does not himself give, that unreality does not lie in either relation as opposed to the other, but in the confusion of any relation with another. It is for lack of this explanation that Locke himself, as we have seen, finds in the liveliness and involuntariness of ideas the sole and sufficient tests (not _constituents_) of their reality; though they are obviously tests which put the dreams of a man in a fever upon the same footing with the ‘impressions’ of a man awake, and would often prove that unreal after dinner which had been proved real before. There is a well-known story of a man who in a certain state of health commonly saw a particular gory apparition, but who, knowing its origin, used to have himself bled till it disappeared. The reality of the apparition lay, he knew, in some relation between the circulation of his blood and his organs of sight, in distinction from the reality existing in the normal relations of his visual organs to the light: and in his idea, accordingly, there was nothing unreal, because he did not confuse the one relation with the other. Locke’s doctrine, however, would allow of no distinction between the apparition as it was for such a man and as it would be for one who interpreted it as an actual ‘ghost.’ However interpreted, the liveliness and the involuntariness of the idea remain the same, as does its relation to an efficient cause. If in order to its reality the cause must be an ‘outward body,’ then it