You and I are different objects; we exist in different places, and at different times. Nevertheless, there are important respects in which we are similar: we are both human beings, for one thing. We are also both English-speaking, with an interest in philosophy. These ways in which we are similar can be expressed in terms of our having the same (or similar) properties: although we are different objects, we are similar to the extent that we share properties. Of course, some objects will be more similar to each other than others: if you are six-feet tall and have brown curly hair, then you will be more similar to me in certain respects than if you are four-feet tall and have straight red hair.
The properties that we have to a large extent determine who we are; they are what mark us out as distinct from other objects. There are a wide variety of different properties that we have: some are biological, such as the parents we have, our eye-colour, and our fingerprints; some are physical, such as our mass or height; others are perhaps more social, such as our nationality, occupation, or marital status. All of these kinds of properties – and many more – have great significance when it comes to determining who we are. Indeed, many people spend a good portion of their lives trying to attain certain properties, whether it be the property of being married, being a Nobel prize-winner, being a parent, being the World Heavyweight Champion, or simply being a good person. In short, the properties we have matter to us.
Properties matter in other cases too. The properties that less sophisticated objects have determine the make-up of the world around us, and the ways that different objects interact. For instance, cars have the property of being metallic, electrons have the property of being negatively charged, grass has the property of being green, and vinegar has the property of being acidic. The myriad different properties that the vast array of objects in existence has, and the ways that those properties interact, is responsible for the way that world is made up.
Or so I would have you believe. For there are some philosophers who think that we can do without properties, and that all this talk of properties is, broadly speaking, a mistake. These philosophers are concerned about the peculiar things that properties would need to be if they were to exist, and propose instead that we simplify things by resisting the thought that talk of properties points us towards the existence of properties. There are two lines of argument here that I will discuss. The first worries that, for all that we have said so far, properties are immensely puzzling kinds of things, so puzzling that many think that they could not possibly exist. The second concerns how seriously we should take our ordinary talk of properties. Let us begin with the first line of argument.
Why are properties puzzling? One batch of reasons has to do with location, and there are two aspects that are of interest to us here. Think about objects again for a moment. For the most part, objects have just one location at any given time, much to the frustration of busy folk who wish that they could be in two places at once. This idea – that nothing can be in more than one place at any one time – is a deep and pervasive aspect of our experience of the world around us; anyone who says that a single thing is in more than one place at a time is usually taken to be speaking nonsense. But now think about properties. We have said that objects have properties, and that the properties objects have mark them out as similar and different to other objects. We have also said that objects share properties, such as you and me sharing the property of being human, for example. If this is the case, though, it seems as though there are things – properties – that exist in more than one place at the same time: the property of being human exists where I am, and it exists where you are too, at the very same time. Properties, then, unlike objects, seem to be multiply located, which to many ears sounds implausible. This is the first worry about location, then: properties seem to exist in more than one place at once, and this just seems odd.
The second worry concerns exactly where properties are located, and is sort of the flipside of the first problem. Just as we ordinarily take it that one object cannot exist in more than one place at once, we also take it that two different objects cannot exist at the same place at the same time. You and I, for example, however close we might be, cannot occupy the very same region of space-time. But now consider the properties that objects have, and where they might be located. Consider some of the properties that I have, such as being male, six-feet tall, carbon-based, and the writer of this article. Where are these properties located? It does not seem to make sense to say that they are each located in different parts of me – my carbon-basedness in my right arm, for example, my being the writer of this article in my left leg – rather, they seem to all exist wherever I as a whole exist. But if this is the case then we seem to have a problem, as it seems as though we have a whole bunch of different things – my properties – that all exist at the very same place at the very same time. This again seems odd.
Properties, then, seem to violate some of the basic principles that we have regarding location, and some philosophers take this to show that properties do not exist at all. But how serious are these problems? We can note that they are based on the idea that we should take principles about the location of objects as a guide to principles about location in general. It is unsurprising that features of the location of objects are the most salient and dominating when it comes to thinking about location, as these are the things we unreflectively encounter and move around in our everyday lives. We can just see and feel that two things cannot be in the same place at once, and that the same thing cannot be in two places at once.
But the defender of properties is licensed to ask at this point why we should take the principles of object location to be principles of location in general. At the very least it seems as though an argument is needed to move from the claim that objects cannot exist in more than one place at once to the claim that properties cannot exist in more than one place at once. Likewise, an argument is needed to move from the claim that two objects cannot exist in the same place at once to the claim that two properties cannot exist in the same place at once. Without any such arguments, at the most these problems just show that properties are different kinds of things from objects, which perhaps is what we should have expected anyway.
So these worries about location, at present, just suggest that properties are different kinds of things to objects, as opposed to showing that there is something incoherent about the existence of properties. Granted, they might be slightly odd entities, with different location conditions than objects, but there seems no obstacle from these considerations at least to thinking of them as entities.
The second line of argument against properties questions whether the ordinary thought and talk I discussed at the beginning really do suggest that we should think that properties exist. The philosophers who push this line of argument want us to think more carefully about what our ordinary thought and talk commits us to. In particular, they want us to think more carefully about the ontological commitments of our speech.
It is undeniable that we often talk about properties – I did so above in terms that I am sure you have heard many people before, and not in the philosophy classroom, but in everyday conversations. When someone says “I long to be married”, they are making reference to a property – the property of being married – which they long to have. When someone says “I’ll have the red rose please”, they are making reference to a property – redness – that the rose possesses. I suggested above that we ought to take this talk seriously in the sense that it points us to the existence of a certain kind of thing – properties – that matter in a variety of different ways.
However, we need to be careful about how literally we take everyday talk, as it is not always a good guide to what exists. Consider, for example, somebody saying “I pulled the plug for John’s sake”. If we are to take this sentence literally, then it seems to suggest that we should take John’s sake to be a distinctly existing object, and presumably the sakes of all other people too. But this seems to be the wrong conclusion to draw: there are no such things as sakes, and what we really mean when we say that we did something “for John’s sake” is that we are did it for John. The addition of a “sake” is merely a rhetorical flourish, and should not be taken literally to imply that there is such a thing as John’s sake, in addition to John himself.
The sceptics about properties that I mentioned above think that a very similar situation occurs in our talk about properties. They think that when we say things like “the rose is red”, we should not take the mention of “red” seriously, just as we should not take the mention of “sake” seriously in the sentence above. When we utter sentences like “the rose is red”, say the sceptics, all we are really committing ourselves to is the existence of an object – the rose – and not the property of being red in addition to it.
However, it is not clear that we can dismiss talk of properties so easily, for, even if the strategy mentioned above worked in those kinds of cases, there are many others where it doesn’t seem as though it would. Consider, for example, the sentence “red is more similar to orange than blue”. This sentence, rather than talking about particular objects, seems to talk about relations between different properties. This creates a problem for the strategy above, as we cannot straightforwardly appeal to objects as the entities the sentence commits us to. Perhaps one available move would be to treat the sentence “red is more similar to orange than blue” as really saying “red objects are more similar to orange objects than blue objects”. This would seem to allow us to just talk about objects, but it carries a prohibitive price, in that it yields a false sentence: it is just not true that red objects are more similar to orange objects than blue objects. For instance, suppose we have three objects: a blue table, a red table, and an orange elephant. According to the solution just proposed, the red table would be more similar to the orange elephant than it was to the blue table, and this just seems wrong!
So, as tempting as it might be to dismiss talk of properties as metaphorical, it is hard to do so. Properties, as odd as they may be, are things which seem indispensable to the way we think about ourselves and the world around us.
If it is the case that we need to posit the existence of properties, what should we say about them? In particular, how should we go about constructing a theory of properties? One way to think about this is to ask the question of what a “Wanted” poster for properties would look like. If we are looking for a dangerous criminal, we collect a description of his or her defining characteristics, with the hope that, using these characteristics, we will find the person who committed the crime. A similar thought can be applied to philosophical theorising, an approach sometimes described as a functionalist approach. The thought with properties is that we collect a description of the defining features of properties, and, once we have done so, this will serve as a guide to constructing a theory of properties: any kind of things we wish to identify as properties will need to exhibit these characteristics.
In what has been said above, we have already made some moves in this direction. At the beginning we noted that properties are the things that make an object the kind of object it is, and ground similarities and differences between objects. They are also things that play a significant role in determining the nature of the world around us in general, as the properties that objects have determine the way different objects relate to each other, and combine together to form other objects. This idea can be understood in a variety of ways, but an influential way to think of it is that properties ground the causal powers of objects. For example, it is because this lump of iron has the property of being metallic that it conducts electricity, and it is because vinegar has the property of being acidic that it turns litmus paper red. In other words, the properties that objects have determine their causal powers. These features are what we might call the metaphysical features of properties. They suggest a very real role for properties in a complete theory of the nature of reality.
We have also noted above a slightly different set of characteristics that we take properties to have. We noted that properties are needed to serve as the things we refer to by certain terms, such as in the case where we have the sentence “red is more similar to orange than blue”. In this sentence, we seem to refer to properties, and make certain statements about them. In a similar vein, we also quantify over properties: when we say things like “those cars are the same colour”, there is something – the same colour – that the cars both are, which we posit the existence of. These features can be described as the semantic features of properties: they are things properties do which we can glean from how we understand the ways we use words.
These two kinds of features – the metaphysical and semantic – join together to give a general set of characteristics that we take properties to have. We can also note that they are not necessarily independent. For instance, we might think that, in certain cases, it is because of the metaphysical features of properties that the semantic features are present. If we think of our thought and talk as responsive to the world around us, we might think that it is because we encounter a certain property – the property of being metallic, say – that we have sentences including the word “metallic” by which we make reference to the property. We might think that this works both ways, and that there are other cases where the fact that we make reference to a property in our thought and talk gives us reason to posit the existence of that property. For example, some of the properties mentioned earlier might fit this bill. We might think that the property of being married, or the property of being a good person, are not properties already “out there” that objects have, rather they are properties that are bestowed upon objects by our own thought, talk, and practices. If this is the case, then there will be cases where the semantic features of properties in some sense ground the metaphysical features. Indeed, if many of the properties we mentioned at the beginning as important to us in our daily lives are to be accounted for, it seems as though something along this line needs to be accommodated.
If we take these thoughts seriously, then it seems as though any good theory of properties ought to take both the metaphysical and semantic features of properties seriously. By doing this can we do justice to the many different kinds of properties that are important to us in our lives and our theories of the world around us. This is indeed a challenge, and something that only fairly recently philosophers have started to take seriously, previously focusing just on the metaphysical features. But it is only by respecting both kinds of features properties have that we can begin to shape a theory of properties that can do justice to the various ways that properties matter.