=2. The Conception of Substance: Hume’s Attack on Theology.= But the association of resemblance has been made the basis of a common illusion. It has been made to transcend its proper sphere of a relationship among inner impressions; and resemblance between ideas has been taken by people generally to mean metaphysical identity or substance. It has been transformed from a relationship between ideas to a relationship between “matters of fact.” Now substance is evidently not an association given with the impressions, like their temporal and spatial order in the association of contiguity, nor is it mere impression of resemblance. Substance is the conception of an unknown, indescribable something back of impressions. There is the conception of the material substance or matter, and the spiritual substance or the soul. How did such illusory conceptions arise? If Hume rejects them as matters of real knowledge, he must nevertheless explain their psychological origin. The illusory idea of substance originates from the similarity of the frequent conjoining of certain impressions. The impressions――sweet, rough, white, etc.――occur together so often that the imagination creates the conception of the substance of sugar behind them. This arises not from the first experience, but after the association of impressions has been observed a large number of times. From the frequent association of ideas arises the _feeling_ of their necessary coexistence. Thus do we come to have the idea of a material substance. Hume evidently follows Berkeley in his criticism of material substance. But Berkeley went only halfway. Berkeley had found that bodies were only conjunctions of sensations, and he had rejected as meaningless the unknown substance behind them. He did not see that the same attack could be made upon spiritual substances. Berkeley’s argument against the substance of the cherry could be used against the Ego or the Soul. Have I the impression of my Ego? Can I touch it or see it? The simple test shows that I know nothing about it, and I cannot affirm whether or not it exists. But if the conception of the Soul has no reality as an object of knowledge, how can it be psychologically explained? How does it arise in the mind? The idea of the Soul is due to the frequent reappearance of the same trains of thought in my mind. Their similarity gives rise to the feeling that a metaphysical identity, or Soul, exists behind them.