People often talk as if nothing were easier than for two naked minds to “meet” or become aware of each other. But I see no possibility of their doing so except in a common medium which forms their “external world” or environment. Even our vague attempt to imagine such a meeting between disembodied spirits usually slips in surreptitiously the idea of, at least, a common space and common time, to give the co- in co-existence a meaning: and space and time are already an environment. But more than this is required. If your thoughts and passions were directly present to me, like my own, without any mark of externality or otherness, how should I distinguish them from mine? And what thoughts or passions could we begin to have without objects to think and feel about? Nay, could I even begin to have the conception of “external” and “other” unless I had experience of an “external world”? You may reply, as a Christian, that God (and Satan) do, in fact, affect my consciousness in this direct way without signs of “externality”. Yes: and the result is that most people remain ignorant of the existence of both. We may therefore suppose that if human souls affected one another directly and immaterially, it would be a rare triumph of faith and insight for any one of them to believe in the existence of the others. It would be harder for me to know my neighbour under such conditions than it now is for me to know God: for in recognising the impact of God upon me I am now helped by things that reach me through the external world, such as the tradition of the Church, Holy Scripture, and the conversation of religious friends. What we need for human society is exactly what we have — a neutral something, neither you nor I, which we can both manipulate so as to make signs to each other. I can talk to you because we can both set up sound-waves in the common air between us. Matter, which keeps souls apart, also brings them together. It enables each of us to have an “outside” as well as an “inside”, so that what are acts of will and thought for you are noises and glances for me; you are enabled not only to be, but to appear: and hence I have the pleasure of making your acquaintance.
Society, then, implies a common field or “world” in which its members meet. If there is an angelic society, as Christians have usually believed, then the angels also must have such a world or field; something which is to them as “matter” (in the modern, not the scholastic, sense) is to us.
But if matter is to serve as a neutral field it must have a fixed nature of its own. If a “world” or material system had only a single inhabitant it might conform at every moment to his wishes — “trees for his sake would crowd into a shade”. But if you were introduced into a world which thus varied at my every whim, you would be quite unable to act in it and would thus lose the exercise of your free will. Nor is it clear that you could make your presence known to me — all the matter by which you attempted to make signs to me being already in my control and therefore not capable of being manipulated by you.