3. The manner in which the imagination co-operates in mental action is this. It presents to the intellect the materials from which that power forms its ideas. When we see, feel, hear, taste, or smell anything by our bodily senses, our imagination takes note of the object perceived by forming a brain-picture of it which is called a _phantasm_. I do not mean to say that it forms a photographic picture of the object; for there can be no photographing taste or smell or feeling; but it forms an image of some kind which it presents to the intellect. This power at once proceeds to form, not a brain-picture, but an intellectual or abstract image of the object presented. For instance, you see this book, and at once you, in some mysterious way which has never yet been explained, impress some image of it on your brain. That you do so is clear from the fact that the image remains when the book is withdrawn. That material image or brain-picture is the _phantasm_. It is not an _idea_, though it is often improperly so called. But your intellect forms to itself an idea of a book; that is, you know what is meant by a book. You distinguish between the mere form of a book and the book itself. Your idea of a book is a universal idea, which stands for any book, no matter of what shape or size. Every phantasm, or brain-picture, is a representation which presents its object as having a definite shape or size, while your idea of a book ignores any shape or size. And yet, when your intellect conceives a book, your imagination will picture some particular form of book. If your brain became so affected by disease as to be unfit for the formation and retention of the proper phantasms, then your intellect either would not work at all or it would work abnormally; your mind would then be insane.