I will try to say something about a profound confusion or blindness which occurs in connection with the notion of mind-independence. What I will say will be reminiscent of some of Wittgenstein's ideas from his mid-late period, especially the ones which influenced Waismann's work on 'language strata' (see references).
This post was prompted by a recent lecture of David Macarthur's, wherein he emphasized that propositions were not linguistic items for Moore and Russell. (Nor, I would add, were they linguistic items (signs) in a projective relation to the world, as in the early Wittgenstein.) Instead, they were supposed to be abstract objects1 which do not in general depend on minds or on language for their existence. This aspect of Moore and Russell's early post-Hegelian thought is often labelled 'Platonism' or 'Platonic realism'. Macarthur wanted to emphasize that this is quite a difficult idea - i.e. to think of propositions as being 'so completely language-independent' (I think he used some such expression).
I want to say: no, not necessarily - this last statement has to be qualified, although it is appropriate enough in connection with the philosophical views of Moore and Russell. I will try to explain what I mean.
We talk of concepts, meanings, propositions, statements and the like. Our talk about these things has a certain logic and grammar; it makes sense to say that a concept is used by somebody, but it makes no sense to say that a concept is three metres away from somebody. It makes sense to call a proposition true, but not red.
I think it is plausible to think of the notion of a proposition, or statement - in something like the sense of 'that which is asserted by a meaningful declarative sentence' - as ordinarily not coming into direct contact with the notion of dependence as it applies to minds and spatiotemporal things. In Wittgensteinian-Waismannian terms, the relevant notion of dependence is part of one stratum of language, and the notion of a proposition is part of another. We don't talk of a proposition depending for its existence on this or that mind, thing, process, etc., any more than we talk of a house being tautological.
At least, this is how it is in the ordinary, or primary language-game. (I think the term 'primary' is perhaps better, since I don't mean to imply that there is anything especially folky about the primary language-games we play with the word 'proposition'.) And this, I believe, is what - in the first instance - makes it correct to say 'Propositions do not depend for their existence on minds', just as it is correct to say 'Houses do not themselves possess arithmetical properties'.
But there is something which makes the statement about propositions significant to us, in a way which the statement about houses is not likely to be. As a piece of grammar, this statement can be said to warn us against a mixing up of language strata which – for reasons which I will not inquire into here – we are especially prone to when philosophizing.
However, 'Propositions do not depend for their existence on minds' is not a reliable guard against this confusion, due to its superficial similarity to non-grammatical statements such as 'The nobility in fourteenth century England did not depend for their existence on the King'. This leads to what might be called a Platonic interpretation of this statement. Rather than being taken as a grammatical warning or prohibition against bringing the mind-(in)dependence concept into direct contact with the proposition concept, these concepts are brought together, and propositions are thought of as, so to speak, being positively independent.
This supports, and is supported by, strange uses of “pictures” of propositions which resemble our pictures of physical objects, ideas of durability and hardness being applied to propositions, Plato's Heaven, and the like. (This is of course very loose talk.) Also, consider the expressions used in this remarkable statement of Russell's in the Logical Atomism lectures: 'To suppose that in the actual world of nature there is a whole set of false propositions going about is to my mind monstrous.'
We should be careful not to confuse the grammatical sense of 'Propositions do not depend for their existence on our minds' with an apparently material sense which arises from a confused mixing of levels (or from a language-game which goes beyond the primary ones we play with 'proposition' and related words).
In the primary game, we simply don't talk about existential dependence on minds in relation to propositions, and this is perfectly in order. That is what is hard to see.
The idea that we simply don't, or can't, talk about propositions (in the ordinary or primary sense) depending on this or that mind, may have an air of quietism and renunciation about it. 'Whereof we cannot speak, thereof we must remain silent' etc. Even worse, it might seem depressingly parochial and conservative. To a great extent, this would be a mistaken reaction. We are not prevented at all from talking about 'propositions' 'depending' on minds - however, if we do so, and if this is anything more than a mere grammatical confusion, then we are simply not playing the primary game.
Despite the anti-metaphysical political stance of the historical antecedents for this sort of view (particularly in the Vienna Circle), I don't see these points as being hostile to philosophical speculation, or the development of new ways of thinking. And perhaps a lot of what is called 'metaphysics' can be thought of as an attempt to develop such new ways of thinking (and talking) about the world. (None of this, by the way, should be taken to imply any sort of Rortian antirealism, excluding considerations of objectivity and correspondence to reality, or anything like that.)
Consider in this connection the growing attention paid by metaphysicians to the way they are using language, especially quantifiers and terms like 'real' and 'exists' (e.g. Hofweber) and also - more relevantly - terms like 'depends on' and 'grounds' (e.g. Schaffer). Investigations into such matters are increasingly common, and often go under the headings 'metametaphysics' and 'metaontology'.
The remarks above are not very well-made, nor are they particularly original. I make them anyway because they seem to embody an important sort of consideration which seems somewhat neglected in contemporary post-linguistic-turn philosophy (although hopefully this is changing).
The relative obscurity of this sort of consideration today has, of course, to do with the fact that it involves something like an analytic-synthetic distinction, or perhaps more like Wittgenstein's arguably non-exhaustive distinction between grammatical and empirical propositions. Such distinctions sit under a dark cloud today. This in turn has to do with the ideas of Quine in 'Two Dogmas' and 'Truth by Convention', and a shift in emphasis toward certain modal notions, arising from Kripke's clear isolation of them.
Cf. this freely available copy of Waismann's article, 'Verifiability', which has some material on language strata. (Note however that one can use the notion of language strata without accepting a verificationist view of meaning.)
Thomas Hofweber (2005). A puzzle about ontology. Noûs 39 (2):256-283.
Thomas Hofweber (2007). Innocent statements and their metaphysically loaded counterparts. Philosophers' Imprint 7 (1):1-33.
Saul A. Kripke (1980). Naming and Necessity. Harvard University Press.
Willard Van Orman Quine (2010). Two dogmas of empiricism. In Darragh Byrne & Max Kölbel (eds.), Arguing About Language. Routledge.
Willard Van Orman Quine (1951). Two dogmas of empiricism. Philosophical Review 60 (1):20-43.
Jonathan Schaffer (2009). On what grounds what. In David Manley, David J. Chalmers & Ryan Wasserman (eds.), Metametaphysics: New Essays on the Foundations of Ontology. Oxford University Press.
Friedrich Waismann (1946). The many-level-structure of language. Synthese 5 (5-6):221 - 229.
Ludwig Wittgenstein (1975). Philosophical Remarks. University of Chicago Press.
Ludwig Wittgenstein (1974). Philosophical Grammar. Blackwell.
1 Or at least partly abstract objects; Russell thought propositions about concrete objects had those concrete objects as constituents.