The most frequent type of objection to the traditional versions of neutral monism is that they are forms of mentalistic monism: Berkleyan idealism, panpsychism, or phenomenalism. The core argument is simple: sensations (Mach), pure experience (James) and sensations/percepts (Russell) are paradigms of non-neutral, mental entities. Hence there is nothing _neutral_ about these neutral monisms. This type of objection—the “mentalism suspicion”—has been articulated by a diverse group of philosophers, among them: (Lenin 1909: 34; Hartshorne 1937: 221–2; Stace 1946; Ayer 1971; Feigl 1958: 426, 1975: 26–7; Maxwell 1976: 354; Popper & Eccles 1977: 199; Strawson 1994: 97; Chalmers 1996: 155; Tully 2003: 355, 369).The _prima facie_ plausibility of this objection is beyond doubt. But Mach, James, and Russell were acutely aware of the problem and took themselves to have responded in a satisfactory manner. They reject the view that a sensation or an experience consists of a subject directing a mental act—awareness, consciousness, acquaintance—onto an object. Dispensing with the subject and the act, they are left with what used to be the object—a red patch, say. And they hold that there is nothing intrinsically mental about red patches. A red patch becomes a red-sensation simply by being appropriately related to other entities of the same kind. There is no quick way to adjudicate this dispute; a careful assessment of each case is required. Still, a comparison of neutral monism with its closest mentalist alternatives can be a useful first step.Panpsychism holds that every basic entity—usually understood as a physical entity—is also a mental entity. The physical nature (if present) and the mental nature of the basic entities are fundamental, i.e., irreducible (to each other or to anything else). On the face of it, panpsychism and neutral monism are strikingly different. Neutral monism takes mental and physical phenomena to be derivative, panpsychism does not; neutral monism holds that basic reality is neutral, panpsychism does not. And neutral monism is compatible with the view that most physical objects, and all their parts, are absolutely nonmental, whereas panpsychism is not. This is how things look on the _Neither View_ of neutrality. On the _Both View_ of neutrality, things are less clear. The most natural reading of the _Both View_ will, however, not yield panpsychism—the view that every basic physical entity has a mind—but a dual aspect view—a view according to which every basic entity has a physical and a mental aspect or side. In any case, Mach, James, and Russell resisted panpsychist or dual-aspect interpretations of their views, though there is evidence suggesting that James adopted panpsychism sometime after 1904.Phenomenalism has been defended as a doctrine about language, about facts, and about things. Taken in this last sense, it attempts to “reduce material objects to sensa, that is, to explain them as consisting solely of sensa or as being primarily groups or patterns of them” (Hirst 2006: 271). We might substitute the terms “sense-data”, “sensations”, “percepts”, “experiences”, etc. for Hirst’s term “sensa”. As noted above, the traditional neutral monists supposedly purged such terms of their usual intrinsically mental dimension. Moreover, neutral monism is not limited to those entities that are sensations, perceptions, and so on—this is particularly clear in the case of Mach and Russell. The existence of vast majority of neutral entities is inferred from the minute set of elements that, due to their causal-functional roles, happen to be sensations and perceptions. These inferred elements are outside of all minds. These are the strong anti-phenomenalist (and anti-idealist) positions. How successfully the various neutral monists defend these claims is, of course, a difficult further question.### 4.3 The Materialism SuspicionIn the past neutral monism has often been interpreted as a form of mentalism. But a number of contemporary philosophers argue that it is best understood as a form of physicalism.We have noted how Landini’s interpretation of the notion of neutrality (according to (3)—the _Possible Constituent View)_ allows him to argue that neutral monism is compatible with physicalism. As he sees it, Russell is committed to such a version of (four-dimensionalist) physicalist neutral monism. Accordingly, Russell is engaged in the project of “constructing both [minds and matter] out of orderings of physical events that are their stages” (Landini 2011: 280). After a detailed discussion, Landini reaches the conclusion that Russell’s basic transient particulars (or events) “are without intrinsic phenomenal character” (Landini 2011: 297). This makes it possible to regard them as physical entities in good standing. Their neutrality consists in the fact that they are the building blocks of both mental and physical continuants (see Landini 2011: 292).Similarly, Erik Banks (see section 5.6 below) presents his so-called “realistic empiricism” as a direct descendant of traditional neutral monism (Banks 2014, viii). But he also holds that his neutral monism is “a kind of physicalism” (Banks 2014: 7, 142). Banks takes himself to follow Russell embracing an ontology of events as manifestations of underlying powers or energies—such as electromagnetism, gravitation, and nuclear forces (Banks 149), as well as neural energies (Banks 2014: 142). But event particulars such as these, Banks insists, “are _so_ physicalistic in nature that there does not seem to be any reason to assume that these natural qualities in physics have anything at all in common with our sensations, which are qualities of a very different order… [involving] events in the human nervous system at a very different scale of complexity and size” (Banks 2014: 156).After a careful survey of the development of Russell’s neutral monism, Donovan Wishon observes that Russell’s post-1940 version of neutral monism “has a greater affinity to Russellian Physicalism than any genuinely _neutral_ monism” (Wishon 2015: 114–5). Among other things, Wishon draws our attention to Russell’s report that “I find myself in ontology increasingly materialistic” (Russell 1946: 700). He also points to Russell’s remarks that “I should regard all events as physical” and that “the distinction between what is mental and what is physical does not lie in any intrinsic character of either, but in the way in which we acquire knowledge of them” (Russell 1958: 12). Hence, Wishon concludes, “mental events will turn out to be a subclass of the physical events that make up reality”—only their special epistemic accessibility distinguishes them from the other physical events (2015: 112). But he does not quite answer whether Russell, in this late period, took all events to be physical due to their intrinsic natures or merely due to their relations to other events.These attempts to combine neutral monism with physicalism, or to reinterpret neutral monism along physicalist lines pose a serious challenge to neutral monism as usually understood. They deny the central claim that the fundamental building blocks of the world are neutral in the sense of being both nonmental and nonphysical.[[18](https://plato.stanford.edu/entries/neutral-monism/notes.html#note-18)] But no less noteworthy is the degree to which these versions of physicalism depart from more standard forms of physicalism. In particular, they agree with neutral monism that physical theories do not fully capture the nature of the world they describe. This suggests that the difference between neutral monism and this sort of physicalism may not be so deep after all (see Chalmers 2015).### 4.4 The Problem of Experience