Because nobody understands what it could mean to 'constitute an object from predicate logic'? An object, after all, is something that one can pick up or weigh, whereas 'predicate logic' is an abstraction. It seems impossible to get from the latter to the former.

That aside the term 'neutral monism' has surely got to be one of the most boring-sounding bits of philosophical jargon ever devised. What springs to mind is a grey-haired man in a grey coat, standing under a grey sky - a 'neutral monist' sky - talking in abstruse philosophical jargon.

What I think it really means, is that reality itself is neither physical or mental, but appears in some aspects as mental, and in others as physical. But what anything could be that could appear in those two apparently divergent ways, is obviously a very difficult thing to fathom.

Hence it is not much discussed.

Bertrand Russell's neutral monism is the view that objects are neither material nor mental. The most important implication of neutral monism is that we can constitute objects surrounding us by predicate logic. It sounds like interesting. However, neutral monism is not much discussed recently. Many philosophers see neutral monism as a kind of dualism. The closest type of neutral monism is David Chalmers' version of dualism. The question is why neutral monism is not much discussed. — mosesquine

On the contrary, evidence suggests that Russellian Monism is enjoying a great deal of interest at the moment. There's even an upcoming international conference in Budapest!

Philip Goff's website is a good place to find out what's going on among the monists and panpsychics:

http://www.philipgoffphilosophy.com/

And here's Galen Strawson arguing in favour of Russellian Monism in the NYT earlier this year:

http://www.nytimes.com/2016/05/16/opinion/consciousness-isnt-a-mystery-its-matter.html?_r=0

I have no particular interest in RM, but keep coming across it. I may have to learn a bit more though as one of the interpretations of quantum mechanics that I'm interested in - Many Minds - seems to share some common themes.

Thanks for useful information.

Actually your old friend Nagel is sometimes 'accused' or credited with a belief in some sort of neutral monism. Have a look at the Stanford entry.

I agree with Tom, there's a revival of interest in neutral monism. I think the variant by a man called John Heil is interesting, but I just happen to have been reading him because he's interested in Mind. His view is certainly neutral monism of a kind, where fundamentals are neither mental nor physical but abstractions. Ordinary objects on his view are 'only modes', that is, 'local thickenings of space-time'. Here's a quote from a book from the Noughties:

Nowadays we prefer to think of the material world as a collection of elementary particles, or fields, or perhaps a single field, a single space–time manifold. On any of these views, macroscopic material objects will consist of arrangements of the ultimate constituents or, if you prefer the idea that the world is a single unified space–time manifold, a way this manifold is. This turns macroscopic objects into modes. — Heil

If we frame things in terms of substance(s), for the purpose of my comments let it be hypothesized that substance is equivalent to information—such that information is what endows anything with any type of form.

[This isn’t something I full-heartedly endorse—potential givens such as Nirvana could, for example, signify information-devoid substance … and I lean toward such presence-endowed (aka existent in the wide sense) given entailed by the concept of Nirvana. Nevertheless, both mind and matter can arguably be reduced to information.]

To run through the list:

Substance dualism then posits that two ontically unrelated types of information co-occur, with most of this view presuming that they also causally interact. This is a no-go for many. So that leaves substance monism as the feasible alternative.

Physicalism then holds that all information is physical; idealism that all information is mental. Both are easy to conceptualize; but—as I’ve discovered through my own trials and errors—the connotations that most assign to idealism can lead to quite a lot of shenanigans; on the other hand, to claim that the universal of a perfect circle, for example, is itself physical information runs against a common set of intuitions held by many, physicalists and non-physicalists alike.

Neural monism comes into play by affirming that what we take to be mind-stuff and material-stuff reduce to (or else are both equivalent to) a neutral type of information—a neutral type of information that in some way holds a duality of property but not of substance: some of it unfolds as mind and some of it unfolds as matter, though it as substance is the same stuff. And in this sense, objects in this view are neither an aspect of mind nor of matter. I haven’t read Russel on this, but I so far don’t think he—or any other neutral monist—would assert that there is no difference between our sensations/intuitions of what is of the mind and what is of matter. The difficulty here is that the mechanisms or means by which this property duality unfolds is anybody’s guess. (I wouldn't say boring so much as not yet comprehensible.) And without some understanding of these metaphysical mechanisms, the notion of neutral monism can easily become a bunch of mumbo-jumbo to many (mumbo-jumbo can also be read as “bullshit”).

That’s why I believe neutral monism hasn’t been in favor historically. Though I’m glad to discover that interest in it is still held by some scholars.