Skin and seeds are proper parts of a tomato, and the tomato is an improper part of itself. But what about such properties as being red, being ripe, being a tomato? Are they parts of the tomato? The very idea will strike many as born of an elementary confusion, as a sort of Rylean category mistake. "Your tomato is concrete and so are its parts; properties are abstract; nothing concrete can have abstract parts." Or: "Look, properties are predicable entities; parts are not. Having seeds is predicable of the tomato but not seeds! You're talking nonsense!"
I concede that the notion that the properties of an ordinary particular are parts thereof, albeit in some extended unmereological sense of 'part,' is murky. Murky as it is, the motivation for the view is fairly clear, and the alternative proposed by relational ontologists is open to serious objection. First I will say something in motivation of the constituent-ontological (C-ontological view). Then I will raise objections to the relational-ontological (R-ontological) approach.
Plainly, the blueness of my coffee cup belongs to the cup; it is not off in a realm apart. The blueness (the blue, if you will) is at the cup, right here, right now. I see that the cup before me now is blue. This seeing is not a quasi-Platonic visio intellectualis but a literal seeing with the eyes. How else would I know that the cup is blue, and in need of a re-fill, if not by looking at the cup? Seeing that the cup is blue, I see blueness (blue). I see blueness here and now in the mundus sensibilis. How could I see (with the eyes) that the cup is blue without seeing (with the same eyes) blueness? If blueness is a universal, then I see a universal, an instantiated universal. If blueness is a trope, then I see a trope, a trope compresent with others. Either way I see a property. So some properties are visible. This would be impossible if properties are abstract objects as van Inwagen and the boys maintain. Whether uninstantiated or instantiated abstract properties are invisible.
Properties such as blueness and hardness, etc. are empirically detectable. Blueness is visible while hardness is tangible. That looks to be a plain datum. Their being empirically detectable rules out their being causally inert abstracta off in a quasi-Platonic realm apart. For I cannot see something without causally interacting with it. So not only is the cup concrete, its blueness is as well.
This amounts to an argument that properties are analogous to parts. They are not parts in the strict mereological sense. They are not physical parts. So let's call them metaphysical or ontological constituents. The claim, then, is that ordinary particulars such as tomatoes and cups have their properties, or at least some of them, by having them as ontological constituents. To summarize the argument:
1. Some of the properties of ordinary concrete material particulars are empirically detectable at the places the particulars occupy and at the times they occupy them.
2. No abstract object is empirically detectable. Therefore:
3. Some properties of ordinary concrete material particulars are not abtract objects. Therefore:
4. It is reasonable to conjecture that some of the properties of ordinary concrete material particulars are analogous to (proper) parts of them.
I grant that the above is not entirely clear, and that it raises questions that are not easy to answer. But does R-ontology fare any better? I don't think so.
Suppose an R-ontologist is staring at my blue cup. Does he see something colorless? Seems he would have to if the blueness of the cup is an abstract object merely related by exemplification to the concrete cup. Abstracta are invisible. Suppose we introduce 'stripped particular' to designate the R-ontological counterpart of what C-ontologists intend with 'bare particular' and 'thin particular.' A stripped particular is an ordinary particular devoid of empirically detectable properties. If the R-ontologist thinks that my cup is a stripped particular, then he is surely wrong. Call this the Stripped Particular Objection.
But if the R-ontologist agrees with me that the blueness is empirically detectable, then he seems to be involved in an unparsimonious duplication of properties. There is the invisible abstract property in Plato's heaven or Frege's Third Reich that is expressed by the open sentence or predicate '___ is blue.' And there is the property (or property-instance) that even the R-ontologist sees when he stares at a blue coffee cup.
Isn't that one property too many? What work does the abstract property do? More precisely, what ontological work does it do? I needn't deny that it does some semantic work: it serves as the sense (Fregean Sinn) of the corresponding predicate. But we are doing ontology here, not semantics. We want to understand what the world -- extramental, extralinguistic reality -- must be like if a sentence like 'This cup is blue' is true. We want to understand the property-possession in reality that underlies true predications at the level of language. We are not concerned here with the apparatus by which we represent the world; we are concerned with the world represented.
In my existence book I called the foregoing the Duplication Objection, though perhaps I could have hit upon a better moniker. The abstract property is but an otiose duplicate of the property that does the work, the empirically detectable propery that induces causal powers in the thing that has it.
So I present the R-ontologist with a dilemma: either you are embracing stripped particulars or you are involved in a useless multiplication of entities.
It's Christmas Eve and there is more to life than ontology. So I'll punch the clock for today. But there are two important questions we need to pursue. (1) Couldn't we reject the whole dispute and be neither a C- nor an R-ontologist? (2) Should ontologists be in the business of explanation at all? (My point that abstract properties are useless for purposes of accounting for predication and property-possession presupposes that there is such a legitimate enterprise as philosophical explanation.)