Secondary Qualities and Possible Worlds
Consider a possible world in which all objects have minds, indeed selves: every physical object is a subject of consciousness. In this world every object has a brain, though the brains might not be very like the brains we are familiar with. Thus trees, rivers, mountains, post boxes, and pebbles all have minds. More precisely, everything that looks like these familiar objects has both a mind and a brain. What is on those minds? Let’s suppose that they are occupied about their own appearance: they perceive the very qualities they instantiate, and maybe nothing else. For example, red objects perceive themselves to be red—as well as any other quality they possess (they taste, smell, hear, and feel themselves too). We humans are aware of many of our own perceptible properties—well, the objects in my possible world are like that too. We can suppose they have this awareness through something like proprioception: they don’t see their own color with a pair of eyes; rather, they sense it inwardly. Our brains could have done the same: they could have made us sense our own color without the need to deploy our eyes, as they make us sense our own bodily posture and movement.  So the objects in my world have a kind of primitive inward awareness of their perceptible qualities: what we see with our senses they sense inwardly with their own organ of awareness—we see an object as red and the red object also perceives its own redness. The set-up is rather like our mental states: others are aware of them by sense perception and inference, and we also are aware of them by introspection. Sensible qualities likewise have a kind of dual epistemology in the world described: they are perceived by other beings and they are perceived by the object with the quality. This seems like a possible world.
There is a question about the nature of these qualities: are they mental or physical or perhaps some third thing? Let’s assume they are mental in some way (we could stipulate it): then the objects in question are sensing their own mental states when they sense their own qualities—they are like us inwardly sensing our aches and pains or sensations of color. An object has the mental quality of being red and it is aware of having this quality. This may be deemed problematic on the ground that colors (etc.) are public properties perceptible by suitable perceivers but mental states are not so perceptible. So there is no possible world in which colors are both mental and perceptible. This doesn’t rule out the possible world I first described, since we could drop the assumption that colors are mental; but it is worth noting that even the world in which colors are mental and perceptible is a possible world. For it is not a necessary truth that mental properties are imperceptible: so there could be a world in which colors are (a) mental, (b) perceptible, and (c) sensed by the object that possesses them. This world would match the description I have suggested for the actual world: our objects instantiate perceptible public qualities that are also sensed by the object that has them and which are mental.  What I am saying, then, is that this is a logically possible world: it contains no contradiction or other conceptual incoherence. The question is not whether it is intelligible but whether it is true. In my possible world I have simply stipulated that the objects have minds and brains that enable them to sense their own perceptible qualities, whereas in the actual world that is very much the question at issue. For now I am only concerned with a theoretical possibility, i.e. whether there is a possible world in which the described set-up exists: and it seems that there is such a world. The objects need not be like ours internally: they could have a far more complex and brain-like interior—they might, indeed, house little brains very like ours that are hooked up to their outward qualities. In this world nature is uniform in the sense that every object, organic or inorganic, has a dual nature, being both mental and physical, both a perceiver and an object perceived. The philosophers in this world might have a dispute about what is true in their world, with one sect insisting on the mindedness of ordinary objects and another sect stoutly denying this (despite being aware of that little brain-like structure in objects). The former group thinks that their preferred hypothesis gives the best overall account of things, while the latter group is resistant to the very idea that ordinary objects could have minds (which by stipulation they do).
Now the question is whether the described metaphysically possible world is also an epistemic possibility for our own world. Can we be certain that our objects lack a mind of their own? I think few will assert that we can: it is an epistemic possibility that all objects have a touch of mind in them. We need not suppose that this mental nature is just like ours, or that of any terrestrial species; it could be quite alien to us, yet still a type of mentality. We must not be parochial about the scope of the mental. Thus, if we have come to the conclusion that colors are mental and hence need a subject to perceive them, we should not be deterred by the objection that colored objects don’t have minds like ours. Our inability to imagine such minds is no objection to the claim that they exist. What about behavior: do objects behave as if they have minds? Again, the question is not easily resolved: organisms as we know them are of many types with very different types of behavior, so we can’t take human behavior as the measure of mentality. A panpsychist will certainly not be moved by the observation that particles don’t behave like humans (or even frogs). There are some who maintain that the physical world is fundamentally mental, but they don’t claim that everything behaves like an animal with a mind. If we have already adopted such a view, we will not be so resistant to supposing that sensible qualities are all mental, and that objects sense their own qualities. True, we have added subjects of awareness to states or events of awareness, but this too is not a radical move once the mentality of matter has been accepted (I am not saying that it should be). We are simply supposing that colored objects are aware of their color; and how could they not be if they are composed of mental states? If red is a mental quality, and all mental qualities need a subject, then we have the result that red objects are psychological subjects. There exist metaphysical outlooks that are quite hospitable to the kind of view I am outlining. But even sans those outlooks we can make sense of the idea that objects possess some sort of subject that perceives their own qualities. It may be a very attenuated type of subject, and its perceptions might be far removed from ours, but it is possible (in both senses) that objects possess such attributes. And if secondary qualities are really mental in some way, then they need some such thing in order to be instantiated. The point I have been making is just that the resulting picture is perfectly feasible as a metaphysical possibility, and can also claim to be an epistemic possibility with respect to our world (it cannot be definitively ruled out). The question then becomes one of overall plausibility and the viability of competing views. My own position is that the view needs to be added to the range of options for consideration and cannot be easily excluded. It is at the least interesting—rather in the way that Berkeley’s view is interesting (which stimulated the present view). Berkeley located the ground of all existence in the infinite spirit that is God; the present view more modestly supposes that all objects have “spirits” within them that perceive the properties they instantiate. Berkeley made room for two types of spirit, the finite spirits of humans and other animals and the infinite spirit of God; the present view allows for the existence of more basic spirits existing in sensible objects. The panpsychist will not be repelled by the very idea of such an expansion, and the view in question is a lot more modest than the panpsychist view (if we allow that some objects lack secondary qualities, e.g. electrons). In any case, the view needs to be evaluated on its merits, its initial strangeness notwithstanding. To me what is compelling is the thought that mental qualities need mental subjects, and colors (etc.) are mental qualities. I think many people (my earlier self included) vaguely assume that colors are mental in some way and that they are possessed by external objects but fail to reckon with the point (insisted upon by Berkeley and later rediscovered by Frege) that mental properties need a subject—that their esse is percipi.  Something has to give once this point is taken in, and one possibility is that the object itself is the source of the needed percipi. We can imagine thinkers that accept that animals have mental and physical attributes but never reflect that the former need a subject, and are indeed naturally opposed to the idea of such a thing; then some radical comes along who argues that the esse of mental properties is percipi, thus forcing an ontological expansion on her colleagues. People have selves inside them too! They aren’t just collections of mental attributes; they need something to perceive these attributes. Well, something like that dialectic can be envisaged for ordinary objects and their qualities, once we accept that they have mental as well as physical attributes. That was the orthodox view among modern philosophers who distinguished primary from secondary qualities; it was Berkeley who pointed out that mental properties (“ideas”) need mental subjects. This changes everything. 
 Let me note that the human body has secondary qualities and hence needs a psychological subject to sense these qualities, given that they are mental. This means that we have more than one mind lurking within us: the regular conscious mind and the mind that exists in the body as the perceiving subject of its secondary qualities. But the proliferation of minds is by now something of a commonplace: the unconscious mind (or several such), the enteric mind, the two hemispheric minds, maybe a bunch of panpsychic minds. Even the conscious mind might consist of several sub-minds, as with modularity. The notion that we have just a single mind seems like a relic of the indivisible immortal soul.
 Of course, the standard assumption is that the subject in question is the human subject, but once this assumption is critically examined its inadequacies quickly reveal themselves (particularly the problem of how colors can exist unperceived).