Men are apt to suppose that these opinions seem reasonable to them merely for the reason that they find in their own experience evidence of their truth. But this is not so. Have we not seen above how long it took men to discover that they must not think of the mind as being a breath, or a flame, or a collection of material atoms? The men who erred in this way were abler than most of us can pretend to be, and they gave much thought to the matter. And when at last it came to be realized that mind must not thus be conceived as material, those who endeavored to conceive it as something else gave, after their best efforts, a very queer account of it indeed. Is it in the face of such facts reasonable to suppose that our friends and acquaintances, who strike us as having reflective powers in nowise remarkable, have independently arrived at the conception that the mind is a nonextended and immaterial substance? Surely they have not thought all this out for themselves. They have taken up and appropriated unconsciously notions which were in the air, so to speak. They have inherited their doctrines, not created them. It is well to remember this, for it may make us the more willing to take up and examine impartially what we have uncritically turned into articles of belief. The first two articles, namely, that the mind is in the body and that it acts upon, and is acted upon by, material things, I shall discuss at length in the next chapter. Here I pause only to point out that the plain man does not put the mind into the body quite unequivocally. I think it would surprise him to be told that a line might be drawn through two heads in such a way as to transfix two minds. And I remark, further, that he has no clear idea of what it means for mind to act upon body or body to act upon mind. How does an immaterial thing set a material thing in motion? Can it touch it? Can it push it? Then what does it do? But let us pass on to the last two articles of faith mentioned above. We all draw the distinction between _substance_ and its _attributes_ or _qualities_. The distinction was remarked and discussed many centuries ago, and much has been written upon it. I take up the ruler on my desk; it is recognized at once as a bit of wood. How? It has such and such qualities. My paper-knife is of silver. How do I know it? It has certain other qualities. I speak of my mind. How do I know that I have a mind? I have sensations and ideas. If I experienced no mental phenomena of any sort, evidence of the existence of a mind would be lacking. Now, whether I am concerned with the ruler, with the paper-knife, or with the mind, have I direct evidence of the existence of anything more than the whole group of qualities? Do I ever perceive the substance?