Moreover, why draw some line between mental and non-mental, particularly given that we don't have a clear concept of what the "physical" is? As Chomsky wrote:
I will be using the terms "mind" and "mental" here with no metaphysical import. Thus I understand "mental" to be on a par with "chemical", "optical", or "electrical". Certain phenomena, events, processes and states are informally called "chemical" etc., but no metaphysical divide is suggested thereby. The terms are used to select certain aspects of the world as a focus of inquiry. We do not seek to determine the true criterion of the chemical, or the mark of the electrical, or the boundaries of the optical. I will use "mental" the same way, with something like ordinary coverage, but no deeper implications. By "mind" I just mean the mental aspects of the world, with no more interest in sharpening the boundaries or finding a criterion than in other cases.
Chomsky is basically arguing that trying to delineate such boundaries as mental/non-mental is on par with delineating the boundary of the “chemical”/non-chemical, "electrical”/non-electrical, etc. From a naturalistic perspective, it’s pointless because common-use terms (ordinary discourse) may not map that well to scientific distinctions.
But, as he says, Chomsky isn't interested in drawing a precise scientific distinction between the mental and the nonmental, claiming that this distinction doesn't have any metaphysical/ontological import. However, he thereby begs the question against those who claim it does. So we are in the midst of a genuinely philosophical debate over the concepts of mentality and physicality. And these concepts are not so hopelessly vague that it is impossible to make any meaningful definitions of them and distinctions between them. However, as for the concept of mentality, the more independent it is of the concept of consciousness/experience, the vaguer it becomes.
I've looked at the debate between Searle and Chomsky on this topic of "unconscious" mental stuff and I don't find Searle's argument convincing. This is summarized in a paper by Peter Ludlow in A. Martinich and D. Sosa (eds.) A Companion to Analytic Philosophy:
Chomsky has also clashed with Searle over the possibility of rules in cognitive science that are “in principle” inaccessible to consciousness. Can there be aspects of the mental which are not “in principle” accessible to consciousness? Searle argues that there cannot. Chomsky (1990, 1994b) argues that the notion of “in principle” in Searle’s argument is vacuous....Chomsky also notes that Searle must introduce the notion of “blockage” to cover those cases in which an individual, perhaps through brain damage, is able to correctly solve a problem, but be unable to say how it was solved. On Searle’s theory, such a person has “in principle” access but suffers from “blockage”. But Chomsky observes that it is entirely arbitrary as to what counts as blockage and what counts as in principle inaccessibility (e.g., perhaps an unfortunate mutation blocked our access to the language faculty). Accordingly, Chomsky argues that such notions have no role in naturalistic inquiry into the nature of the mental (and indeed, cognitive science rightly ignores such notions).
But then you might argue that why should we even consider such unconscious or 'tacit' knowledge as being "mental"?
I haven't yet formed an opinion about the distinction between in-principle inaccessibility and blocked accessibility; but as for your question, one can indeed go one step further and doubt or deny the mentality of so-called mental dispositions (dispositional mental properties) such as knowledge, beliefs, desires, preferences, interests, intellectual skills, which are unconscious as long as they are unmanifested, i.e. not part of the present (affective, cognitive, or conative) content of one's consciousness. If one considers consciousness to be the mark of the mental, then this step is logical.
Nevertheless, in this case one can still distinguish between those nonmental phenomena which are premental and those ones which are not: A nonconscious neural disposition is premental
iff its manifestation is a conscious experience, otherwise it is non-premental. Of course, this turns "premental" and "preconscious"/"pre-experiential" into synonyms. We then have two basic sorts of mental phenomena: conscious
ones (= experiences) and preconscious
ones (= mental dispositions). Preconscious phenomena are nonconscious but "conscifiable", i.e. they can become conscious phenomena, being accessible to consciousness.
Because we have zero idea how such properties can be constructed of neurons and the like. Whereas, the more abstract models put forth by linguists/cognitive scientists do offer explanations:
In the present case, the theories of language and mind that seem best established on naturalistic grounds attribute to the mind/brain computational properties of a kind that are well-understood, though not enough is known to explain how a structure constructed of cells can have such properties.
This is not to deny that in the future we may come to understand such stuff from a neurophysiological perspective. Alternatively, such a perspective may never be adequate because it may turn out to be mistaken; that is, we may be in the same boat as chemists were in the previous century before the advent of QM which overthrew Newtonian mechanics. The chemist's abstract models proposed were considered 'useful fictions' by the physicists of that time because they could not be accommodated by the physics of the time. It turns out that the chemists were right. The physics was just wrong. With the advent of QM, unification between chemical and physical was then, to a large extent, established. So the argument is that just because some of these more abstract models proposed by linguists/cognitive scientists cannot be unified with our present conception of the neurophysiological/neurons/cells/neural networks, etc. doesn't tell us that these models are incorrect or unfruitful, particularly since they provide much more adequate explanatory function than the neurophysiological.
According to cognitive science, there are nonconscious mental processes which are "computations over mental representations". But if the brain doesn't really work like a computer and there aren't really any mental items with semantic properties in the nonconscious, nonconsciously active sphere of the brain, then the question is what makes such a fictional model explanatorily useful and fruitful when the "theoretical entities" postulated by cognitive science, i.e. nonconscious (and "nonconscifiable") mental images, concepts, propositions, rules (algorithms), are in fact nonentities. How can reality be accurately and correctly explained by a model which mis
Anyway, even if those inherently nonconscious mental processes as postulated by cognitive science existed, they couldn't be known to exist, because they'd be neither externally, third-personally perceptible nor internally, first-personally perceptible (introspectible). That is, if they existed, they would be perceptually, experientially inaccessible in principle. Are scientists qua scientists allowed to believe in entities for which there can be no empirical evidence? Of course, if the cognitive scientists admit that their model of the mind represents a fictional world rather than the real world, then they are free from any serious ontological commitment to their "theoretical entities". (But then, again, the question is how the real can be explained in terms of the fictional, the unreal.)