THE ANSWER TO THE FOURTH LETTER.

“Sir,”

“My being out of town most part of the month of January, and some other accidental avocations, hindered me from answering your letter sooner. The sum of the difficulties it contains, is (I think) this: That it is difficult to determine what relation the self-existent substance has to space. That, to say it is the substratum of space, in the common sense of the word, is scarce intelligible, or, at least, is not evident; that space seems to be as absolutely self-existent as it is possible any thing can be: And that its being a property of the self-existent substance, is supposing the thing that was to be proved. This is entering indeed into the very bottom of the matter, and I will endeavour to give you as brief and clear an answer as I can.

“That the self-existent substance is the substratum of space, or space a property of the self-existent substance, are not perhaps very proper expressions, nor is it easy to find such: But what I mean is this: The idea of space (as also of time or duration,) is an abstract or partial idea, an idea of a certain quality or relation, which we evidently see to be necessarily-existing; and yet, which (not being itself a substance,) at the same time necessarily presupposes a substance, without which it could not exist; which substance, consequently, must be itself (much more, if possible,) necessarily-existing. I know not how to explain this so well as by the following similitude: A blind man, when he tries to frame to himself the idea of body, 430his idea is nothing but that of hardness. A man that had eyes, but no power of motion or sense of feeling at all, when he tried to frame to himself the idea of body, his idea would be nothing but that of colour. Now, as, in these cases, hardness is not body, and colour is not body; but yet, to the understanding of these persons, those properties necessarily infer the being of a substance, of which substance itself the persons have no idea: So space to us is not itself substance, but it necessarily infers the being of a substance, which affects none of our present senses; and, being itself necessary, it follows that the substance which it infers, is (much more) necessary.

“I am, Sir,

“Your affectionate Friend and Servant.”

Jan. 29, 1713.