In relation to substance, therefore, the attributes must be apprehended as entirely independent: they must be conceived through themselves: their conception is not dependent upon that of substance. This is necessarily true; for since the substance can have no determinateness, then the attribute which is its determinate being, cannot be explained from the substance, but only through itself. Only by apprehending the attribute independently can the unity of the substance be maintained. In relation to each other, the attributes are to be taken as opposites strictly and determinately diverse. Between the bodily and the ideal world there is no reciprocal influence nor interaction: a body can only spring from a body, and an idea can only have an idea for its source. Hence, therefore, neither the mind can work upon the body nor the body upon the mind. Nevertheless there exists between the two worlds a perfect harmony and an entire parallelism. It is one and the same substance which is conceived under each of the two attributes, and under which one of the two we may contemplate it is indifferent to the substance itself, for each mode of contemplation is equally correct. From this follows at once the proposition of Spinoza, that the connection of ideas and of things is the same. Hence the solution to the problem of the relation of body and soul, so difficult to find from the Cartesian standpoint, is readily seen from that of Spinoza. Body and soul are one and the same thing, only viewed under different attributes. Mind is nothing but the idea of body, _i. e._ it is the same thing as body, only that it is viewed under the attribute of thought. In the same way is explained the apparent but not real influence of the body upon the mind, and the mind upon the body. That which, in one point of view is bodily motion, in another is an act of thought. In short, the most perfect parallelism reigns between the world of bodily things and that of ideas.