certain nature to mind Locke could not have given an account of 

 the origin of human knowledge, he could have ascribed any other 

 desired qualities to the mind necessary in order to obtain an ex- 

 planation ; and, if by ascribing certain powers to spirits Hyslop could 

 not have accounted for the phenomena to be explained, he could, at 

 will, have assumed the spirits to have other powers, and have adapted 

 the assumed nature of spirits to the requirements of the case. 



When, however, the assumption is that a thing out of experience 

 is like something in experience, the nature of the thing in experience 

 whose qualities we know, limits and controls our assumption. When 

 it is assumed in the theory of ions that an atom consists of a spherical 

 shell of electrification, surrounding a number of negatively charged 

 particles, it cannot be or it is not assumed that an atom has any 

 different or other qualities than such a spherical shell of electrification 

 containing charged particles would have. Our assumption is limited 

 and controlled by our experience with such electrically charged 

 bodies; and if the qualities which we, by experiment, find such bodies 

 to have, will not, when ascribed to the atom, explain the phenomena 

 in question, the theory will be abandoned or modified by assuming 

 the atom to >e like some other thing in experience whose qualities 

 we know. From the nature of the assumption that matter is electrical, 

 the theory will be abandoned, if the qualities of electricity discovered 

 by experiment fail to explain the characteristics of matter; and from 

 the nature of the assumption that an atom is an electrically charged 

 spherical surface containing negatively charged particles, the theory 

 of such atoms will be abandoned, if the qualities which by experi- 

 ment we know such an electrically charged surface containing such 

 negatively charged particles would have, fail to explain the relation- 

 ships described by the periodic law. But the nature of the as- 

 sumption of the existence of spirits and their powers is such that 

 the theory need never be abandoned. As spirits are assumed to be 

 like nothing in experience, their powers must also be assumed, and 

 any powers may be ascribed to them necessary to explain any given 

 phenomena. When new phenomena are revealed, spirits can be as- 

 sumed to have different or additional powers and the theory, there- 

 fore, need never 'be abandoned. The assumption of Locke's theory ^ 

 is of the same nature. If the mind is like nothing in experience, any 

 powers may be ascribed to it, and any phenomena explained by it. 

 So much for the distinction between the use of assumption in theories 

 like the theory that matter is electrical and the theory of ions and its 

 use in theories like the theory of discarnate spirits and the theory of 

 mind as set forth by Locke. 



The theories examined, then, divide themselves into two classes, 



[17] 



