The predicate IS has two parameters. Placing arguments in those parameters produces something like the following Relation:
|Car With Serial Number 1235813||Red|
|Rose With Barcode 3185321||Red|
|Grain Of Salt Mentioned By Hegel||Cubical|
|Grain Of Salt Mentioned By Hegel||White|
This is a SINGLE relation, one may note, just as INVITES and TO_THE_LEFT_OF are. But while the relations INVITES and TO_THE_LEFT_OF are fairly easy to get one’s mind around, IS is a more difficult case. What is the relation between a property and the thing of which it is the property? Should we say that the property “inheres” in the thing? (Whatever “inheres” means.) Should we follow Plato and think of the relation between thing and property as analogous to the relation between reflection in the mirror and the thing or person reflected? So that the thing is a wholly relational entity wholly dependent upon something more real that exists independently, i.e., the property existing as a Platonic Form? Should we be more Aristotlean and think that, while yes, a given property (e.g. RED, e.g. PRIME) is one thing, not many, it is always already “contracted” (the ‘contracted’ business always makes me think of the old freeze-dried instance coffee commercials … the property gets “sucked” into the thing accompanied by the corresponding sound) ala John Duns Scotus into (but where does the ‘into’ come from? Does this mean ‘inhere’?) the thing so that it never exists independently of the thing? So that it has a “unity less than numerical?” (Source of the ‘unity less than numerical’ thing comes from some writing of Duns Scotus which I do not remember.) Should we think, along with William of Ockham, that it is nonsense to think of a single thing, e.g., the property RED, as existing in several places at the same time, so that we have to think of the red of the car and the red of the rose petal as in fact two different properties, even if they exactly match the same color sample held by the Interior Decorator? (So that ‘Red’ in the Relation above would always have to be marked by a number serving as an index?)
Or maybe the Relation IS is not a real Relation at all, but an artifact of a Word. Given the Word ‘is’, we think there is a corresponding Predicate generating Propositions which, when true, form a Relation. But in reality there is no such Relation. Perhaps?