"The subject of the present Volume, although replete with interest, and of much practical importance, is one as to which we have no means of obtaining such complete and definite knowledge as to admit of it being presented in the shape of a systematic treatise. Some points may be considered as established with a sufficient degree of certainty; there are others as to which opinions may reasonably differ; while there is still a greater number as to which we must be content to acknowledge that, with our limited capacities, we have no means of forming an opinion at all. The method of dialogue seems to be especially adapted for inquiries of this description; and it is hoped that this will be considered as a sufficient apology for the form in which the following observations are submitted to the public. One of my correspondents seems to be of opinion that I have not sufficiently regarded the dignity of human nature in speaking of the minds of the inferior animals as belonging to the same mode of existence, or being of the same essence, with the mind of man. I do not myself see how any one, who does not (with Descartes) believe animals to be mere unconscious machines, can arrive at any other conclusion. I do not, however, feel that it is necessary for me to enter further into the question, as it has been fully considered by one of much greater authority than myself; and I have only to refer to the observations on this subject contained in the first chapter of the Rev. Dr. Butler's Analogy of Religion to the Constitution and Course of Nature"--Preface. (PsycINFO Database Record (c) 2010 APA, all rights reserved).