In one of his last writings on logic, Peirce returned to the difference between reality and externality. According to the CP editors, this was written for the 1908-9 Monist series ‘Some Amazing Mazes’, but not published at the time. I would recommend reading the whole text beginning at CP 6.318, but that's a bit much for a blog post, so i will jump to CP 6.327-8:
What is meant by calling anything real? I can tell you in what sense I always use the word. According to my use of it, there is a certain resemblance between the Real and the External which renders the discrimination of each from the other important for right reason. Any object whose attributes, i.e. all that may truly be predicated, or asserted, of it, will, and always would, remain exactly what they are, unchanged, though you or I or any man or men should think or should have thought as variously as you please, I term external, in contradistinction to mental. For example, a dream is mental, because it depends upon what passed in the thoughts of the dreamer whether it be true that the dream was of a dog or was of the Round Table of King Arthur or of anything else. On the other hand, the colors of objects of human experience and in particular the contrast between the color of the petals of a Jaqueminot rose and that of the leaves of the bush, although it is relative to the sense of sight, is not mental, in my sense of that word.
[I omit here Peirce's discussion of the ‘difference between a color and a sensation of color’.]
Color, therefore, is a quite remarkably vague quality, as well as being relative to the normal sense of sight. If by ‘normal’ were meant merely the average (or any other kind of mean) of actually occurring instances, say the average sensation of all the inhabitants of the globe on a certain date, then this might have been modified by some disease affecting a large part of the people who happened to be living at the time; and since ‘color’ refers to normal chromatic sense, it would depend upon what passed in the minds of a certain body of men. But, in fact, the ‘normal’ is not the average (or any other kind of mean) of what actually occurs, but of what would, in the long run, occur under certain circumstances. Now what would be, can, it is true, only be learned through observation of what happens to be; but nevertheless no collection of happenings can constitute one trillionth of one per cent of what might be, and would be under supposable conditions; and therefore, though it might conceivably prevent many generations from rightly determining what is normal, it could not affect the true – and ultimately ascertainable (provided there were anybody to ascertain it) – mean and normal; and thus, the result is that no such accident could affect the normal or the true color. So, in general, what I mean by the external might vary with how persons of a given general description would think under supposable circumstances; but it will not vary with how any finite body of individuals have thought, do now think, or will actually think.
So much for what I mean by the external. The main difference between the external, as I use the term, and the real, as I employ that term, seems to be that the question whether anything is external or not is the question of what a word or other symbol or concept (for thinking proper is always conducted in general signs of some sort) is, I say, a question of what a symbol signifies; while the question of whether anything is real or is a figment is the question what a word or other symbol or concept denotes. If the attributes of or possible true assertions about an object could vary according to the way in which you or I or any man or actual body of single men, living at any time or times, might think about that object, then that object is what I call a figment. But if even although its attributes, or what is true of it, should possibly vary according to what some man or men might think, yet if no attribute could vary between being true and being false, according to what any plural of single men could think about that thing, then, and though it were accordingly not external but mental, it would nevertheless be real, since precisely that is what I mean by calling an object real.
This might have some bearing on the question Ben posed in the Addendum to his message: ‘what would be the practical difference between the immediate object and the dynamic object of a TRUE proposition?’ My guess is that there would be no difference at the end of inquiry, but the difference does make a difference in the actual practice of inquiry, because that process can never be known to have reached its end, which is truth itself.
I have another question arising from Peirce's Berkeley review, specifically his comments about Kant's view of reality as Peirce describes it there and in some later writings. But i'd better save that for another post.