Does Diaphaneity refute SDT?

Harman, Tye, Martin et al on diaphaneity and sense data

Some modern critics of SDT argue against it on the grounds that it cannot be reconciled with the so-called "Diaphaneity" or "Transparency" of experience. The Diaphaneity Thesis derives from G.E. Moore, in his celebrated paper "The Refutation of Idealism" (1903). I shall, below, argue that the critics are wrong and that SDT is compatible with Diaphaneity -- as long as the doctrine is understood in a way that is faithful to Moore's fundamental position. I shall argue that modern commentators, particularly though not exclusively advocates of Intentionalist Representationalism, present as Diaphaneity what is, in fact, a corollary to it, given additional assumptions. As we shall see, the additional assumptions simply beg the question against sense datum theory.

Some, though not all, Intentional Representationalists have appealed to Diaphaneity as a positive argument for their own position and, assuming the incompatibility of IR and SDT, thereby indirectly argue against SDT. Other critics who appeal to Diaphaneity to argue directly against SDT include Direct Realists (Disjunctivists), Functionalists and others.

Moore On Diaphaneity

In his "Refutation of Idealism", Moore inserted into his main line of argument a digression which was intended to explain to the reader, not so much the logic of the Idealist position, but why it might be easy for the Idealist to come to believe it. His explanation introduced the Diaphaneity Thesis. The explanation was at once both psychological and metaphysical; it reflected the contingencies of our mental lives, and a fundamental division in our place in the world.

Essential to Moore's account of sensation was his insistence that

in every sensation or idea we must distinguish two elements, (1) the ‘object,’ or that in which one [sensation] differs from another; and (2) ‘consciousness,’ or that which all have in common – that which makes them sensations or mental facts. (444)

contrary to the Idealist for whom “what is experienced is held to be identical with the experience of it” (445). Something could turn from green to brown, but our consciousness of them remains an unvarying element. The problem was that the second element reveals nothing of itself; consciousness was, "as it were", diaphanous or transparent.

This was important for Moore because, in his view,

the most striking results both of Idealism and of Agnosticism are only obtained by identifying blue with the sensation of blue: that esse is held to be percipi, solely because what is experienced is held to be identical with the experience of it.

Moore proposed that his contemporary Idealists (after Berkeley and Mill) had fallen prey to this conflation, and he gives two pieces of evidence for the plausibility of the claim. The first, which is problematic and curious, is the claim that

language offers us no means of referring to such objects as 'blue' and' green' and' sweet,' except by calling them sensations: it is an obvious violation of language to call them, things' or ' objects' or ' terms'. ... But it is hardly likely that if philosophers had clearly distinguished in the past between a sensation or idea and what I have called its object, there should have been no separate name for the latter. They have always used the same name for these two different, things (if I may call them so); and hence there is some probability that they have supposed these' things' not to, be two and different, but one and the same. (446)

Despite the curiosity of this argument's premises, I think that it is fair to say that the problem that Moore recognized lingers today in the literature on conscious, and I shall return to the issue later.

More importantly for our immediate discussion, Moore's second plausible consideration is that

when we refer to introspection and try to discover what the sensation of blue is, it is very easy to suppose that we have before us only a single term. The term , blue' is easy enough to distinguish, but the other element which I have called' consciousness '-that which sensation of blue has in common with sensation of green-is extremely
-difficult to fix. That many people fail to distinguish it at all is sufficiently shown by the fact that there are materialists.
And, in general, that which makes the sensation of blue a mental fact seems to escape us; it seems, if I may use a
metaphor, to be transparent -- we look through it and see nothing but the blue; we may be convinced that there is
, but what it is no philosopher, I think, has yet clearly recognised. (446)

It is, perhaps, understandable that some philosophers have not been able to 'isolate' consciousness sufficiently to form a clear conception of it, because they

have not been able to hold it and blue before their minds and to compare them, in the same way in which they can compare blue and green. And this for the reason I gave above: namely that the moment we try to fix our attention upon consciousness and to see what, distinctly, it is, it seems to vanish: it seems as if we had before us a mere emptiness. When we try to introspect the sensation of blue, all we can see is the blue: the other element is as if it were diaphanous. (450)

Moore's point is that what is presented to us in consciousness contains no attributes of consciousness itself.

Remarkably, Moore qualified this claim of sheer diaphaneity or transparency by allowing that consciousness "can be distinguished if we look attentively enough, and if we know that there is something to look for". He was dismissive of his own attempt to explain the matter: "My main object in this paragraph has been to try to make the reader see it: but I fear I shall have succeeded very ill." (450) That seems a fair judgement, given that he offered no hint about what properties consciousness revealed of itself to itself.

To clarify his position, Moore raised the question of whether a sensation of a blue flower might actually be blue, too. He proposed that, even if the sensation were blue, it would be irrelevant to what such a sensation was of. Such a sensation would be only incidentally blue. A sensation of blue could be blue, red, magenta, plaid, or, presumably, devoid of any colour at all. In Moore's vocabulary, as ill-fitting as it may be for current philosophical usage, a sensation could have as its 'content' the property of blueness quite independently of its being a sensation of blue. What determined what it was a sensation of was what it had as its 'object', not its 'content'. Independently of whatever other properties it had, the key one a sensation of blue had to have was

a perfectly distinct and unique relation to blue, a relation which is not that of thing or substance to content, nor of one part of content to another part of content.

To say that the relation of a sensation of blue to blueness was the same as the relation of a blue bead to blueness would be wrong. Such a "content theory"

entirely fails to express the fact that there is, in the sensation of blue, the unique relation between blue and the other constituent. And what I contend is that this omission is not mere negligence of expression, but is due to the fact that though philosophers have recognised that something distinct is meant by consciousness, they have never yet had a clear conception of what that something is. They have not been able to hold it and blue before their minds and to compare them, in the same way in which they can compare blue and green. (450)

The explanation for the philosophers' inability to hold consciousness "before their minds" and make the comparison with blue is that consciousness is “as if it were diaphanous”, that is, "transparent".

A sensation is, in reality, a case of ‘knowing’ or ‘being aware of’ or ‘experiencing’ something. (From a more modern perspective, whether 'knowing' should be in there is controversial, but that will not matter for our present discussion.) However, Moore moved on from saying directly what a sensation really is, to explaining what fact is known, when we know that the sensation of blue exists? The answer is “that there exists an awareness of blue”. This awareness, he says, is “something distinct and unique, utterly different from blue”. Further, it has:

a perfectly distinct and unique relation to blue, a relation which is not that of thing or substance to content, nor of one part of content to another part of content. (449)

The relation of awareness to the blue that the sensation if of is neither that of substance to attribute nor of attribute to attribute in a given substance.

On the other hand, the 'incidental' blue would be only an attribute of the sensation, inhering in it as in a ‘thing’. Moore called the collection of attributes inhering in a thing the 'content' of the thing. The incidental blue is not the ‘object’ of the awareness element of the sensation; it is not in the proper unique and distinct relation to it to be its object.

From this we learn, I think, that, for Moore, we could not be aware of any of the attributes of an experience without their being relata in the 'unique and distinct relation'. Further, we learn that because experience is transparent we learn that none of the attributes of the sensation meet that requirement.

When, by appeal to introspection, we look for "what the sensation of blue is", the blue "is easy enough to distinguish" but the consciousness is "extremely difficult to fix". It -- what "makes the sensation of blue a mental fact" -- "seems to be transparent", "as if it were diaphanous".

So experience fails to disclose to us the properties of consciousness itself that permit it to serve as the second element of sensation. There is a unique and special relation to the blue that is apparent to us but, presumably, that relation does not hold for properties of the consciousness itself. No given sensation is reflexive in that respect, engaging its own properties.

It seems also that consciousness is oblivious to not only those attributes that enable its discharging of its role in sensation, but also to those which are inessential to it, the 'incidental' blue, for example, of Moore's thought experiment. I think I am right to think that the 'incidental' blue is not a feasible candidate for being an attribute which serves the consciousness role. And I think that Moore offers some hint that he thought the same.

For, as Moore summarizes:

When we know that the sensation of blue exists, the fact we know is that there exists an awareness of blue. And this awareness is not merely, as we have hitherto seen it must be, itself something distinct and unique, utterly different from blue: it also has a perfectly distinct and unique relation to blue, a relation which is not that of
thing or substance to content, nor of one part of content to another part of content. (29) (emphasis added)

I draw the conclusion from this that the properties that are constitutive of consciousness are not different from blue in the way, for example, that red, orange, magenta or brown are different from it, but rather as being of an utterly different kind. It's noteworthy that Moore tells us that it is the element of consciousness that makes sensations what they are as "sensations or mental facts". (444) Consciousness is "that which makes the sensation of blue a mental fact". (446) What sort of attributes consciousness has that contributes the mentality Moore doesn't tell us.

"Refutation" not a sense datum theory

Moore’s doctrine of the diaphaneity of experience is fundamentally a negative thesis; it is the denial of the availability to introspection or attention of the properties of our sensations. It is the absence of discernible properties of sensations that is the key explainer of why, according to Moore, the Idealist finds it easy to run together, say, ‘sensation of blue’ and ‘blue’. However, that is not to say that Moore did not think that important positive claims followed about was discernible and discerned by introspection and attention.

A number of years after the publication of “Refutation”, Moore celebratedly (or notoriously) embraced sense datum theory, eventually equivocating between different variants of the position. One variant seems to have conceived of sense data as ‘inner’ or subjective elements. A later version conceived of sense data as ‘outer’ or objective facing surfaces of bodies in the external world (similar to the view of "Refutation", as we shall see). Eventually Moore reverted to the "inner" model. A number of modern authors seem to take it for granted that Moore had embraced the sense datum theory by the period during which he wrote "The Refutation of Idealism". I think that he had not. At the very least, there is good reason to think that Moore did not there assume a sense datum theory of the ‘inner’ kind in giving his account of diaphaneity. Thus, for example, in the concluding paragraphs of the paper, he categorically asserted that

I am as directly aware of the existence of material things in space as of my own sensations; and what I am aware of with regard to each is exactly the same – namely that in one case the material thing, and in the other case my sensation does exist. (453)

It is likely that Moore had not at that time looked closely into the question of illusions and hallucinations.

The key point

Such an apparent Direct Realism with respect to "material things in space" does not fit well with sense datum theory of the 'inner' kind. However, regardless of the timing of Moore's adoption of the sense datum theory, it should be plain that his thesis of diaphaneity is, in fact, independent of whether the ‘objects’ of sensations are ‘inner’ or ‘outer’ ones. Whether we are aware of an ‘inner’ blue or an ‘outer’ blue, it is the 'awareness' that the doctrine of diaphaneity is about: what our introspection or attention reveals is only the blue and not attributes of the being aware itself.

Even if Moore, at the time of writing "Refutation", believed that the blue 'object' of a sensation was the blue of a flower outside his body, it makes no difference to the standing of the thesis that the awareness in our sensation does not reflexively capture its own properties and yield them in the experience of the subject.

If experience really is diaphanous, then our expectations for solving the problem of consciousness need some adjustment. For the issue is not just that of explaining phenomenal qualities, but rather that of explaining, whether scientifically or philosophically, if that is something different, the reality of awareness -- consciousness -- as an unobservable.

Moore’s version of diaphaneity is, then, at the outset, the negative thesis that our being aware of an instance of blue does not includeour being aware of (any attributes of ) the awareness itself.

Strikingly, on the other hand, modern philosophers who appeal to diaphaneity, prominently though not exclusively including some advocates of Intentionalist Representationalism, tend to put the doctrine in terms of its arguable corollary that introspection yields awareness only of the attributes of the external world, give or take. (Leave aside phosphenes, migraine castellation, dreams, and night-time noise to signal.) We are aware, they say, of properties of represented external worlds, not attributes of our experience. This is a logically much stronger position than what I have suggested Moore's to be even though Moore, as I have indicated, may have, when writing "Refutation", agreed with modern philosophers that the blue in question, in a sensation of blue, is the blue of an external object, that fact is not what the core doctrine of diaphaneity is about. Diaphaneity is about awareness, not about what awareness is of per se.

Why consider blue in the sensation?

It may seem intuitively obvious that we should, but we might profitably pause to ask why, with Moore, we might be considering the question of the sensation's incidental blueness. Why is it philosophically natural (if any questions are natural when they concern sensations) to ask whether a sensation of blue is blue as well as the perceived external blue object.

There are elements of the philosophical tradition that offer suggestive precedents.In the Aristotelean and Scholastic tradition, the assumed models of perception were committed to there being sensible qualities of external things which were enabled by certain states of the intervening media to be instantiated in the appropriate sensory organ of a perceiving subject. For example, redness in a tomato might be instantiated in the subject's eye. Thus, the very qualities of external things appear in the perceiving subject, too, though in numerically distinct instances. The philosophical tradition clearly suggests the legitimacy of asking whether perception involves the duplication of outer instances of qualities by inner instances of them.

More importantly, the literature on sense datum theory in modern times also makes it sensible to examine whether there are inner duplicates of outer qualites. I think that we can only understand why recent criticisms of sense datum theory take the form that they do if we take into account some idiosyncracies of prominent versions of the theory published in the second half of the 20th century. Some classic sense datum theories seemed to deny such duplication; one of Russell's sense datum theories opted for the idea that external things were logical constructions out of sense data, so there was, one supposes, only one locale -- a private space -- for the instantiation of sensible attributes. But, more recently, other prominent sense datum theorists (e.g., Frank Jackson) have offered accounts that seem to suggest that we see external visual objects by seeing inner visual objects, which invites the duplication interpretation.

Harman and the case of Eloise

In the modern literature, what is usually taken to be the Diaphaneity Thesis first reappeared influentially (though not under that name and without any citation of Moore) in Gilbert Harman's paper, “The Intrinsic Quality of Experience” (1990). There, Harman inveighed against those who think that so-called "qualia", certain intrinsic, non-intentional qualities of experiences, are irreconcilable with a functionalist theory of perception and mind. Harman's argument denies that there are there are such attributes of experiences. He also expressly rejected the sense datum theory by appeal to what are, in effect, Diaphaneity considerations.

SDT should be rejected, Harman proposed, because it fails to“distinguish between the properties of a represented object and the properties of a representation of that object.” He observed:

The notorious sense datum theory of perception arises through failing to keep these elementary points straight. According to that ancient theory, perception of external objects in the environment is always indirect and mediated by a more direct awareness of a mental sense datum.

Essential to the SDT picture is awareness of the attributes of sense data, understood as elements of the given experience. And it is this awareness of elements of the experience that Harman's argument denies. Someone looking at a tree, say, "is aware only of the intentional or relational features of her experience, not of its intrinsic nonintentional features”.This means that she is aware of "the properties of a represented object", not "the properties of a representation of that object".This claim is, in effect, a claim of Diaphaneity, denying that the perceiving subject is aware of attributes of her experience and asserting that she is aware of the attributes of what the experience is of -- its intentional object. According to Harman, "she has no access at all to the intrinsic features of her mental representation that make it a mental representation of seeing a tree". The absence of any such access undermines the sense datum theory.

We can see in Harman’s discussion the claim that the fact of Diaphaneity or, at least, the positive corollary to Moore’s negative thesis, argues against the sense datum theory.

Harman's discussion does not quite match up with Moore's because Moore espoused a sort of direct realism in sensations. Hence the sensation of blue implicated a blue in a flower nearby. Harman's version of the implicit Diaphaneity Thesis is that the perceiver is aware, not of properties of the sensation, but rather the properties of the intentional object -- what the experience is a representation of. This allows Harman, unlike Moore in "Refutation", to accomodate illusory or hallucinatory objects, even if at the cost of invoking a doctrine of intentional objects which don't exist.

Harman's discussion calls SDT into question because it denies that perceivers are aware of properties of their experiences.

Martin versus SDT

M.G.F. Martin has proposed explicitly that the fact of the diaphaneity of experience is problematic for SDT. Though himself a Disjunctivist (Naive Realist), Martin concurs with the Representationalist position that "we cannot introspectively attend to the properties of our experience", and observes that:

the concern is that introspection of one's perceptual experience reveals only the mind-independent objects, qualities and relations that one learns about through perception. The claim is that one's experience is, so to speak, diaphanous or transparent to the objects of perception, at least as revealed to introspection. (378)

He has noted "a common objection" to sense datum theories, which is:

they cannot give an adequate account of the fact that introspection indicates that our sensory experiences are directed on, or are about, the mind-independent entities in the world around us, that our sense experience is transparent to the world.

Martin, M.G.F., "The Transparency of Experience", Mind & Language 17:4(2002), 376-425, p. 376.

Martin's target is SDT's which assert:

that experience is entirely subjective in character, that it involves awareness of certain non-physical or mind-dependent entities, sense-data which are not to be identified with objects in the world around us, or the awareness of certain subjective qualities, qualia or sensational properties. (377)

"Such experience", Martin asserts "is not of a mind-independent world and is not representational in character". Further,

[t]he diaphanous character of experience would seem to indicate a lack of evidence for the existence of sense-data at a point where one would expect to find it. (378)

Naive Sense Datum Theory (NSDT), the preferred view of this site, does not fit the terms of the first disjunct of Martin's description but may fit the second. The sense in which NSDT has it that experience is subjective in character is complex and ambiguous, but sense-data are not assumed to be non-physical, though they may be "neo-physical". They may not be mind-dependent; although they are, indeed, not "in the world around us" in the sense that they are outside our bodies, they are in the physical world, in the brain. Experiences, in which sense data have a role, are often "of a mind-independent world", and can be representational in character, though less than one might initially suppose. Each of these points deserves considerable elaboration, but my priority here (as was Martin's in the article cited) is to examine the significance of what Martin referred to as "transparency" for sense datum theory.

Intentionalist Representationalism and Diaphaneity

Sense datum theorists, particularly those who share the central assumptions of NSDT, should reject Martin's implication that diaphaneity undermines the evidence for their position. The main reason is that as formulated by modern intentionalists the doctrine of diaphaneity simply begs the question against sense datum theory. NSDT and similar theories insist that what is given in experience is not the external world but some array in the mind / brain. We are never consciously aware of distal stimuli.

We may be able to "learn about" external things through perception, but we do not do so because they are presented to us in consciousness. It is appropriate to add, contra Martin, that what is consciously revealed to us is not counter-evidence against SDT but positive evidence for sense data. It exhibits properties which we cannot credibly attribute to external things. For example, the distinction between unique and binary hues, displayed in the phenomenal array, has no physical foundation in the distal world, and so the variegation of such hues in our experiences becomes part of the body of evidence for saying that it is not coloured external objects but coloured internal objects we are aware of.

Extrospection is inner awareness

In the texts that I have quoted above, Harman and Martin both seem to suggest that what should trouble the sense datum advocate is the failure adequately to explain the character of introspection in the context of the perception of external things. Thus Harman implies that if SDT were right then, when seeing some external object, a tree in his example, making an attentional shift from extrospection to introspection should reveal the "intrinsic features of your visual experience". But, he says, it does not; it reveals only "features of the presented tree". Similarly, Martin insists that "we cannot introspectively attend to the properties of our experience".


Harman's and Martin's critique seem to me to talk past the sense datum theorist, and it certainly does not refute SDT. For NSDT and other variants of SDT, it is the attributes of sense data that we are aware of in extrospection, not the attributes of trees and toys and so on. Our experience has, as components, arrays of sense data that we typically mistake for the external world (in what I term "The Grand Stimulus Error"). Those arrays are, in all likelihood, in the brain of the viewer. When Harman, Martin, and others adopt their line of argument, they fail to recognize that, according to these sense datum theories, the difference between extrospection and introspection is not the difference between inspecting external things and inspecting internal things. It is an attentional shift in the inspection of internal things. That shift may lead to a variety of alterations in the qualitative character of the phenomenology, perhaps giving greater prominence to sensations standing for the zone around the head, attending to the blurry shape that stands for the side of one's nose, monitoring subvocalized speech, and noting emotional tone, to give several illustrations. However, typically, the subject will not lose awareness of, say, the yellow which flags the Bumblebee Transformer or the green associated with the leaves on the tree. It is this residual continuity between extrospection and introspection that the critics of SDT mistake for evidence that "introspection of one's perceptual experience reveals only the mind-independent objects, qualities and relations that one learns about through perception", as Martin puts it. The essential point is that the intentionalists' diaphaneity argument to the conclusion that we are not aware of the properties of our experiences fails to recognize the starting point of the sense datum position, which is that, not only are we aware of properties of our experiences, but everything we are aware of is properties of our experience -- specifically, those of our sense data.

Early in the observations above, I proposed that the modern notion of diaphaneity to which intentionalists like Harman and Tye have appealed is not precisely the one that Moore identified. For the moderns, the defining characteristic of diaphaneity is that what is disclosed to the perceiver is the distal world plus some bodily sensations and the like, all of which are distinct from any attributes of the relevant experience itself. There is a case for saying that, in "Refutation", Moore, too, took experiences to reveal the external world, although some commentators presume that he was a sense datum theorist at the time he wrote it. Even so, what is important is that the defining characteristic of diaphaneity was not the assumed revelation of the external world; that was, arguably, a corollary of the definition and other assumptions. The defining characteristic was the difficulty in finding any awareness of the factor that was common to all sensations, independently of the variegation in their content: the relation of 'being conscious of'. In his famous example, what was missing was “something distinct and unique, utterly different from blue”. It was:

a perfectly distinct and unique relation to blue, a relation which is not that of thing or substance to content, nor of one part of content to another part of content. (449)

Bluntly, Moore's diaphaneity was the near impossibility of being aware of the properties of being aware.

What can we say about the issue of diaphaneity in relation to SDT? We have seen that Martin and others have argued that awareness' being diaphanous in the modern sense -- roughly speaking, that we are aware only of the external world, and not of any properties of our sensations -- implies that SDT is wrong. But that is not a substantive argument against SDT; it is simply and only a denial of the SDT starting position.

There is still an important issue about whether, for SDT, awareness is diaphanous in Moore's sense? In answering this, I repeat the following claim about what constitutes an experience according to SDT: experience is a composite of sense data, the awareness relation of subject and sense data, and other constraints which contribute to determining what attributes of the sense data are 'projected' onto the object of the experience and how precisely the representation functions. If awareness is diaphanous in Moore's sense, then we should say that the subject is not aware of any attributes of the condition of awareness, only those of the sense data which is the vehicle for projecting content.

Of course, we cannot say a priori that awareness is not reflexive. Moore claimed that in exceptional circumstances we can discover awareness but he gave no hint of what the circumstances were and what was discovered. So, whether he had in mind that an individual act of awareness had itself as part of its object, or not, is not readily establishable.

If a single act of awareness did reveal its own attributes reflexively to itself, then we might say that the disclosed properties were both awareness and sense datum, thus blurring the division of labour between the two. That should not present a difficulty for the sense datum theory, although it does suggest that it should not permit what I have elsewhere here termed 'exhaustive projection' of the phenomenal character of what the subject is aware of. Phosphenes, after-images and the like seem to indicate that some properties of sense data, more familiar to us than any properties of awareness itself, already establish that exhaustive projection is not generally in play.

Moore proposed that the object of sensation routinely changed, while conscious awareness was invariant across sensations. Given that, most of the time, we are unaware of the properties of awareness, it's not clear what Moore thought the grounds were for saying that consciousness was a constant across all sensations. We might, perhaps anachronistically, reconstruct the position by defending the idea that awareness is constant across all sensations but assuming that we suffer periods of inattention which explain the seeming diaphaneity of awareness when applicable. Another possibility is awareness without incurring short term memory at the microscopic temporal scale. Some models of hemineglect are similar to that idea and it may be the right way to think of some cases of inattentional blindness or change blindness.

Ultimately, my point here is to urge the idea that when we look for ways in which we think that diaphaneity might fail we will do better service to Moore's intent, understand better what he meant, if we do not content ourselves with the analysis of examples like those given by Martin, Kind, and others. In those examples, introspection reveals attributes of our experiences which are, in a sense, just 'more of the same'. Diaphaneity can fail more interestingly than by matching an experienced outer object's yellow with an awareness of an iinner yellow which is a property of the experience. That would, indeed, constitute a failure of diaphaneity, and is, logically, a perfectly good counterexample. But it's not really an instructive one for reflecting what Moore had in mind. It's a contrary, but it's a red herring. Better, though anachronistic as an interpretation of Moore's thought, would be having an awareness of, say, a certain electron cloud with suitable electrical potentials which constitute, let's suppose, the field of awareness addressing a yellow object of that awareness. That would be something very unfamiliar and, if qualitatively at all, qualitatively very different from red, white, and blue. Yellow is not an instructive contrary; the intrinsic qualities of a given electron cloud which is our condition of awareness make a more instructive contrary.

Sartre's coffee: finding the suggestive contrary

It's not "we don't experience an inner yellow by introspection while we do experience a yellow toy", but rather "we don't experience the properties of the special relation of consciousness that holds between the sensation and its object" that better catches Moore's point.

In terms more reminiscent of STD, Moore is saying that, in a given sensation, we are not aware of the act of awareness, only the object.

In making the contrast of the two contraries above, I am reminded of a vaguely philosophical joke about J.-P. Sartre. Sartre, on Boulevard St. Germain, fancied a black coffee, and, sitting down in his favourite cafe, asked the waiter to bring him "a coffee without milk". The waiter left, but returned shortly and said to Sartre, "I'm sorry, Professor, we're out of milk. Would you mind having your coffee without cream".

Moore wanted his sensation without consciously discernible consciousness. I contend that Martin, Harman, Tye, Kind, Pautz, and others, in effect, take Moore to want his sensation without discoverable blueness. It's true that Moore carefully considered whether there might be blueness in the sensation. He had discussed it only subjunctively, to emphasize that blueness in the sensation, had there been any, would have been utterly irrelevant to what the sensation was of, its object, and, further, to repudiate the Idealist's conflation of being blue and being a sensation of blue.

Diaphaneity prohibits a sensation's having as its object any of the properties that make it mental. Being blue is not an aspect of the mental. That's the reason Moore introduced Diaphaneity into a paper refuting Idealism.

(to be continued)