Reading this same truth in the forms of matter, we may say that species will not pass into higher species without the intervention of a force distinct from either. The impulse which adds a new attribute must be intellectually separable from all those pre-existing, and its material representation must be physically distinct from pre-existing forms. This complete separability precludes the possibility of mere physical genesis. The added attribute is presented by a new form of matter, revealing the presence of a new thought--a new effect, requiring the agency of a new cause. In accordance with the usual economy of nature, who never duplicates her forces, change will be made only so far as may be necessary to communicate the additional idea. Organisms representing previous thoughts will be added to, in order to express the expansion of the thought, instead of a creation _de novo_ in each instance. Thus an identical cellular structure will be found in all organic beings, from the lowest to the highest, each higher type carrying forward the idea and its physical expression found in the lower. The differences between no two terms in the series can be total, nor can any two terms be identical, as each higher species will embrace all the attributes of the lower, differing only by the addition of others. This is simply the physical expression of the logical truth that whatever can be predicated of the genus can be predicated of every individual contained under it. As the individual is only the expansion of the genus, so higher physical types must also be similar expansions of lower. Here, then, is evolution, or development: primarily an evolution of the generic into the individual, the continued differentiation of a generic idea through successive individualizations, each adding to the previous group of attributes, thus rendering the idea increasingly complex; and, secondly, an apparent physical evolution or development, interpreting this logical process by a series of physical forms so related as to reveal the relation existing between the thoughts thus interpreted. In the physical representation of the ideas so related, there must be an apparent physical evolution--that is, the process of evolution logically must, like the ideas thus evolved, have a physical expression, and the successive steps in this logical evolution must be revealed by material forms bearing an analogous relation, and thereby expressing the logical process. Matter is nothing, so far as we are now concerned, but the condition necessary to the objective expression of thought. Every phase of matter is simply an objective formulation of a corresponding phase of thought. Every addition to form implies an antecedent increase of thought, as there can be no formal expression until there is something to be expressed. There can, then, be no such thing as mere material evolution, for whatever is material is only symbolical.