Now all these propositions are, I think, typical propositions of the sort which we call propositions about physical objects; and the two coins themselves _are_ physical objects, if anything is. My question is: _In what sense_ are these propositions true?
And in considering this question, there are, I think, two principles which we can lay down as certain to begin with; though they do not carry us very far.
The one is (_a_) that the upper side of the coin, which I am said to _see,_ is not simply identical with the visual sensible which I _directly apprehend_ in seeing it. That this is so might be thought to follow absolutely from each of the two facts which I have called (_b_) and (_d_); but I am not quite sure that it does follow from either of these or from both together: for it seems to me just possible that the two sensibles in question, though _not_ circular _in my private space,_ may yet be circular in _physical_ space; and similarly that though the sensible of the half-crown is smaller than that of the florin _in my private space,_ it may be larger _in physical space._ But what I think it does follow from is the fact that another person may be seeing the upper side of the coin in exactly the same sense in which I am seeing it, and yet his sensible be certainly different from mine. From this it follows absolutely that the upper side of the coin cannot be identical with _both_ sensibles, since they are _not_ identical with one another. And though it does not follow absolutely that it may not be identical with _one_ of the two, yet it does follow that we _can_ get a case in which it is not identical with _mine_ and I need only assume that the case I am taking is such a case.
From this it follows that we must distinguish that sense of the word "see" in which we can be said to "see" a physical object, from that sense of the word in which "see" means merely to directly apprehend a visual sensible. In a proposition of the form "I see A," where A is a name or description of some physical object, though, if this proposition is to be true, there must be some visual sensible, B, which I am directly apprehending, yet the proposition "I see A" is certainly not always, and probably never, identical in meaning with the proposition "I directly apprehend B." In asserting "I see A" we are asserting not only that we directly apprehend some sensible but also something else about this sensible--it may be only some proposition of the form, "and this sensible has certain other properties," or it may be some proposition of the form "and _I know_ this sensible to have certain other properties." Indeed we have not only to distinguish that sense of the word "perceive" in which it is equivalent to "directly apprehend," from _one_ sense in which we can be said to perceive a physical object; we have also to distinguish at least two different senses in which we can be said to perceive physical objects, different both from one another and from "directly apprehend." For it is obvious that though I should be said to be now seeing _the half-crown_, there is a narrower, and more proper, sense, in which I can only be said to _see_ one side of it_--not_ its lower side or its inside, and not therefore the whole half-crown.