This materialistic way of accounting for the origin of the human mind necessarily excludes the idea of its separate creation or its distinctive character. The theory is perfectly consistent with itself, in supposing that the mind of man does not differ in kind, or differ fundamentally, from those exhibitions which in the lower animals lead us to attribute to them some mental power. But whether the theory is consistent with what we know of our own minds, as compared with what we can observe in the other animals, is the real question. In the first place, it is to be remembered that we can read our own minds, by the power of consciousness and reflection. In the next place, it is conceded that we can know nothing of the minds of the other animals, excepting by their outward actions. They can not speak, to tell us of their emotions, their memories, their fears, their hopes, their desires, what they think, or whether they think at all. They do acts which wonderfully resemble the acts of man, in outward appearance, as if they were acts which proceeded from the same power of reason but in a less perfect degree; yet they can tell us nothing of their mental processes, if they have such processes, and the utmost that we can do is to argue from their acts that they have mental faculties akin to those of men. It is in the ordained nature of things that we know and can know, by introspection, what our own minds are. We can know the mind of no other animal excepting from his outward acts. How far these will justify us in assuming that his mind is of the same nature as ours, or that ours is an advanced development of his, is the fundamental question. Plato was evidently led, by that study of the human mind which is open to all cultivated intellects through the process of consciousness and reflection, to conceive of the soul as a created intelligence of a spiritual nature. The fanciful materials out of which he supposes it to have been composed were the mere machinery employed to express his conception of its spiritual nature and its indestructible existence. He was led to employ such machinery by his highly speculative and constructive tendencies, and because it was the habit of Greek philosophy to account for everything. Some machinery he was irresistibly impelled to employ, in order to give due consistency to his theory. But his machinery in no way obscures his conception of the nature of the soul, and we may disregard it altogether and still have left the conception of a spiritual and immortal being, formed for separate existence from matter, but united to matter for a temporary purpose of discipline and trial.