For our purposes, the main lesson of this paper is that the sorts of logico-linguistic issues about proper names that we have been discussing are not just issues about language. They are intimately tied up with epistemological issues about the nature of our cognitive relationship to the world. That is what makes them interesting. In particular, although "On Denoting" is concerned primarily with logical issues concerning definite descriptions, it is clear that epistemological themes are just under the surface. This paper makes those more explicit and makes it clear what is really motivating Russell.
The topic is "what it is that we know in cases where we know propositions about 'the so-and-so' without knowing who or what the so-and-so is". This is a question about, as Frege might have put it, the "objective content" of our knowledge: about what proposition (or, in Frege's language, Thought) we know in such cases. So, in that sense, it is a question about the logical structure of cognition. But the reason the question is important is because it is really a question about the nature of our cognitive relation to the world.
Russell contrasts cases in which we know an object only by description with cases in which we are acquainted with the object of our knowledge. For the moment, we may think of the basic case of acquaintance as perceptual awareness. So, sitting at my desk, I am visually aware of my keyboard, so that would be a case of my being acquainted with it.
Note that Russell seems to be exploiting here an ambiguity in the English word "know". Other languages have different words for these two notions. But in English, we speak of knowing facts (Sally knows that snow is white), and also of knowing objects (Sally knows John). It is this latter sort of knowledge that one has "by acquaintance" or "by description". Russell's question then is: How does whether one knows an object by acquaintance or by description affect the sort of knowledge (in the knowing facts sense) that one can have about it?
Russell implicitly takes the distinction between acquaintance and description to be exhaustive. (See e.g. p. 110.) I.e., he assumes that, for any given object about which we can think, we must either be acquainted with it or else know it by description. We shall consider at some length later whether this is true.
What reasons might there be to think that the distinction between acquaintance and description was exhaustive? Is it plausible that it is?
Russell suggests, on pp. 109-12, that there are several sorts of things with which we can be acquainted: (i) sense-data, by which he means particular elements of sensory experience, such as color-impressions and sounds; (ii) oneself (which conclusion is reached on pp. 110 by arguing that one could not merely have descriptive knowledge of oneself); (iii) universals, including properties and relations.
On the other hand, Russell denies that we are ever acquainted with physical objects (e.g., my keyboard) or with other minds, insisting that we can only ever know such things by description. Russell does not actually argue for this claim, but it is clear enough from the text (e.g., p. 114) that Russell thinks we are never really perceptually aware of people, say, but only with "certain sense-data" that, perhaps, we are caused to have by that person. And Russell thinks one is never really aware of an entire coffee cup, say, but at most with certain of its surfaces, and even then only with sense-data one is caused to enjoy by light bouncing off those surfaces, or whatever.
As a result, Russell says, "proper names are usually really descriptions". Exactly what does he mean by this claim?
Russell's extremely narrow view of the scope of acquaintance is an optional feature of his overall view: One could think the distinction between acquaintance and description was important but draw the boundaries of acquaintance different from how Russell does. Indeed, in many ways, a recurring theme in many of our later readings will be what sorts of cognitive and perceptual relations to things support knowledge about them that is "direct" in the sense Russell thinks knowledge by acquaintance is "direct".
Russell goes on to argue that, if we know an object only by description, then the knowledge we have about that object is, in a sense, not really knowledge about that object at all. Rather, if we fully "analyze" what we know, we find that it is "directly" about things with which we are acquainted, and that the object we know by description enters only as the value of a variable: the x that is uniquely so-and-so.
At the end of the only full paragraph on p. 116, Russell raises a question about the nature of communication that is strikingly reminiscent of a footnote about "Aristotle" in "On Sense and Reference". How are Frege's and Russell's attitudes towards this issue under discussion similar or different? Or is it not the same issue?
This discussion motivates what Russell calls "[t]he fundamental epistemological principle in the analysis of propositions containing descriptions", and which he states as: Every proposition which we can understand must be composed wholly of constituents with which we are acquainted" (p. 117).
Russell says that it is "plain why [he] advocate[s] this principle". So this should be an easy question: Why does he? Feel free to discuss the argument on pp. 117-8 in answering the question.
Russell says that his "fundamental principle" just amounts to saying that "we cannot make a judgment or a supposition without knowing what it is that we are making our judgment or supposition about". Is that right? What unstated premises might be in play here?
Russell then illustrates the consequences of this principle for the analysis of proper names (pp. 118-21), arguing along the way that the principle does not imply that our judgements are really about our "ideas". (It would be interesting to compare Frege's and Russelll's treatments of this issue.)
There then follows a lengthy discussion (pp. 121-7) that recapitulates central points from "On Denoting". It constitutes a response to a paper by Emily Elizabeth Constance Jones, who had herself published a reply to Russell's criticisms of Frege. Those criticisms, the most central of which is the Gray's Elegy argument, have not been our focus, so we probably will not spend much time on this part of the paper. But anyone who is interested in the Gray's Elegy argument will want to read Jones's paper and study these parts of "Knowledge by Acquaintance" carefully.