Büchner. I fancy that space is nothing but the volume of bodies.
Reader. How is this possible? A body moves through space. Now, does a body move through its own volume, or does it move through the volume of other bodies? On the contrary, the body cannot move without pushing away before it all other bodies and volumes whatever from the space they occupy. It is therefore evident that space, as such, is not the volume of bodies.
Büchner. Then I shall say that space is the capability of bodies and motion.
Reader. This definition of space may be admitted if properly understood. But what is such a capability? Is it, in your opinion, a real and positive entity?
Büchner. I should not think so, unless, indeed, it be occupied by bodies.
Reader. I know that many are of this opinion, that the reality of space depends on the presence of bodies; but I say that, if such were the case, then empty space would be mere nothing. Now, if you admit this, you will be compelled to admit also the absurdity that a mere nothing can be greater or smaller. For between two neighboring atoms there may be a greater or smaller interval of space; and such an interval, by the hypothesis, would be nothing. Hence it is evident that space, no matter whether occupied or unoccupied, must be something real.
Büchner. Then I say that space is a mere relation of material objects.
Reader. There are relations of bodies in space; but all such relations presuppose the existence of absolute space, and therefore space itself is none of those relations. Moreover, since all real relations have their reason in something real, which is the foundation of the relativity, it follows that space, as that through which one body is really related to another, is in itself a reality, independently of the relations which may result from the existence of bodies in it. And again, before bodies can be considered as related through space, they must be each located in space. But, evidently, they cannot be located in space if there is no space. And therefore there must be space before any local relation of bodies can be imagined as possible. Hence you cannot maintain that space is a mere relation.
Büchner. Perhaps I shall be obliged to say with Kant that space is only a subjective form of the mind.
Reader. Then you will entangle yourself still more. The assumption would imply the denial of all real distances, of all real volumes, of all real movements, of all real phenomena, and of all natural laws. For if space is only a subjective form of our mind, then there is no space out of the mind; and consequently there are no real distances and no real movements in the outside world, and science becomes an array of lies.