Skip to main content
SearchLoginLogin or Signup

This is the Question: To Be or Not to Be?

An Introduction to Ontology

Published onAug 24, 2021
This is the Question: To Be or Not to Be?

1 • Introduction1

Ontology designates the area of philosophical reflection that circles around the words that occur twice in the one Shakespeare quotation that everybody knows even when they haven’t read Hamlet: ‘to be’, the equivalent of which is ‘to exist’, and is usually considered to be a part of metaphysics. The central ontological question, as the American philosopher Willard V.O. Quine has famously said, is “What is there?” Part of an answer to which could be “there is the number 5” or more generally, “there are numbers” (or “numbers exist”). Part of an answer could also be “there are rocks” or more generally, “there are material objects (they exist).”2 If Quine has formulated the central ontological question, then there is a question that logically precedes it, i.e. “What is existence?” or, alternatively, “What is it for something to exist?”. Since the question is about the meaning of ontology’s central concept, it can be called the “meta-ontological question”. It is natural to think that we need an answer to the meta-ontological question if we are to fruitfully approach the ontological question. Accordingly, in this chapter I will consider both the meta-ontological and the ontological question. Within the space of this chapter, the treatment will necessarily be brief, but it will be enough to get a sense of the main topics in ontology, as well as of various approaches to the meta-ontological question.

2 • Is there a property that everything that exists has?

I start with the meta-ontological question “What is it for something X to exist?” or, alternatively, “Is there a feature or property such that everything that exists has it, and that in order for something to exist it has to have it?” Let us consider the following answer: a thing exists provided it is physical—and let us call this view physicalism. “To be” and “to be physical”, according to friends of physicalism, are two names for the same property. If we say that “X exists”, then, the physicalist holds, we say no more and no less than that “X is a physical thing”.

This answer is instructive because of two different responses it can (and should) elicit, a semantic and an epistemological one. The semantic response - having to do with the meaning of words - is as follows: the two terms “to be” and “to be physical” might refer to the same set of objects, yet can have different meanings. We must distinguish between the meaning of a term and the objects to which the term applies. The meaning of the word ‘dog’ lists properties that an animal must have in order to be a dog. This is called the intension of the word ‘dog’. This is different from its extension: that is the set of objects to which the term applies, the set of dogs. Two terms can have the same extension but different intensions, e.g. the terms ‘having exactly and only three sides’ and ‘having exactly and only three angles’ have obviously different intensions: they are intensionally diverse. But they are extensionally equivalent, i.e. the set of things to which the one term truly applies is identical to the set of things to which the other term truly applies. One response to physicalism is along these lines: it says that even if “to be” and “to be physical” are extensionally equivalent, this doesn’t mean that these terms are also intensionally equivalent. If the two were intensionally equivalent, they would be synonyms in the way taxi and cab are synonyms. But “to be” and “to be physical” just aren’t synonyms. When we say “X is a taxi” and “X is a cab” we say the same thing about X. But when we say “X is” and “X is physical”, in the latter statement something is predicated of X that just isn’t predicated of X in the former statement. “To be” and “to be physical”, unlike “is a taxi” and “is a cab”, are not intensionally identical, they aren’t synonyms. Indeed, Hamlet didn’t say that the question is to be physical or to not be physical! But the physicalist may still be right: “to be” and “to be physical” may be extensionally equivalent—that is, everything that exists may in fact be something physical. This leads up to the second, epistemological, response that physicalism should elicit, viz. “how did you, physicalists, figure out that everything that exists is something physical?—how did you arrive at the conclusion that ‘to be’ and ‘to be physical’ are extensionally equivalent?” This is by no means an easy question for physicalists to answer. For they surely have not figured this out in the way chemists have figured out that water is H2O, and astronomers have figured out that the Eveningstar is the Morningstar—that is, not through some form of scientific research.

Physicalism isn’t the only view that elicits (and should elicit) the two responses mentioned. Every view that says that “to be” just is “to be F” (where “to be F” stands dummy for possible views like “to be in time-space”, “to stand in causal relations to other things”, “to be concrete”, “to be mental”) should elicit the semantic and the epistemological responses.

The conclusion we can draw is that any claim to the effect that “to be” is “to be F” is problematic. That is to say, any answer to the question that is the title of this section (“Is there a property that everything that exists has?”) and that has the form “yes, there is such a property, viz. property F”, is problematic. What can, perhaps, be said is that everything that exists has the property of existence—and that this is the best answer we can give to the question at hand. I say “perhaps”, for the 18th century philosopher Immanuel Kant has famously argued that this cannot be right, since existence, as he contends, is not a property.

3 • Is ‘existence’ or ‘being’ a property?

Kant’s denial that ‘existence’ is a property can be illustrated as follows. Suppose we are asked to sum up the properties of the Eiffel tower. Then we will likely mention that it is made of mainly iron, that it is over 300 meters high, that it has four legs, that it is located on the left bank of the Seine, that its official opening was in 1889, and that in recent times it is yearly visited by over 6 million people. But shouldn’t we add to this list “that it exists” as well: isn’t “existence” one of the properties of the Eiffel tower too? As indicated, Kant says we should not. His reason is this: in order for something (whether it is the city of Köningsbergen, the President of the U.S., or the Eiffel tower doesn’t matter) to have properties at all, it should exist. Only things that exist can have properties. And hence, Kant held, “existence” just isn’t a property.

It would seem that Kant’s line of thought is unobjectionable, except for the last step. It is unobjectionable that “existence” cannot be added to the list of properties of the Eiffel tower. It is unobjectionable that the Eiffel tower can only have properties because it exists. But it is objectionable to conclude from this that “existence” is therefore not a property.

Let me explain. Kant held that “existence” is not a property of things—i.e. of substances like the Eiffel tower. But from this it cannot be concluded that it is not a property at all. For we can think of “existence” as a property not of things, but as a property of a set of properties (and this may even be what Kant himself held). For example, consider the following set of properties: “is made of mainly iron”, “is over 300 meters high”, “has four legs”, “is located on the left bank of the Seine”, “was officially opened in 1889”, and “is in recent times yearly visited by over 6 million people”. Then we can say that to affirm that the Eiffel tower exists, is to affirm that this set of properties has the following property: the properties in this set are the properties of one thing. This illustrates how we can think of “existence” as a property—a property not of individual things, but of sets of properties.

We should take note of the fact that this explanation of how we can think about “existence” as a property, included a numeral, i.e. the number “one”. The 19th century German mathematician and philosopher Gottlob Frege made the striking and valuable observation that there is a deep connection between the notion of “existence” and the notion of “number”. His observation has been captured in the slogan that affirmation of existence is denial of the number zero. What the slogan aims to express can best be explained by examples. To say that planets exist, is to say that the number of planets is not zero. To say that there are female prime ministers, is to say that the number of female prime ministers is not zero. And if we say that there are no winged horses, we say that the number of winged horses is zero.

Frege’s slogan gives us a handle on how to understand affirmations of the existence not only of kinds of things (planets, prime ministers), but also of individual things, such as the Eiffel tower or the painter Holman Hunt. The slogan suggests the following. To say that the Eiffel tower exists, is to say that the number of things identical with the Eiffel tower is 1. And to say that Holman Hunt exists, is to say that the number of things identical with Holman Hunt is 1.

Now, if we take Frege’s slogan on board, we can even think about existence as a property of individual things. If the Eiffel tower exists, then the Eiffel tower’s existence is this property: the number of things identical to it is 1. And if there is a tallest man in South Dakota, then that man’s existence too is the following property: the number of things identical to it is 1.

Seen from this perspective, the conclusion, then, is that Kant’s conclusion that “existence” is not a property must be qualified.

4 • Are ‘existence’ and ‘being’ the same notion?

In the opening paragraph I said that “to be” and “to exist” are synonyms, have the same meaning. But this has been denied by, among others, the late 19th century Austrian philosopher Alexius Meinong. He claimed that “to be” and “to exist” are different notions. If he is correct, this would mean that the sentences “There are black holes” and “Black holes exist” say different things. The distinction enabled him to say that there are things that don’t exist—examples of which would be the President of the UK and the 24th child of Henry Kissinger. The President of the UK should then thought to “be”, although his or her “existence” should be denied (the UK has no President, and never has had one). Likewise, the 24th child of Kissinger should be thought to “be”, albeit that his or her “existence” should be denied (Kissinger having no 24th child).

One argument philosophers have advanced to buttress the distinction between “being” and “ existence” is that it enables us to say such things as “The President of the UK doesn’t exist”—which, it is claimed, can only make sense if the President of the UK can be referred to, which requires in turn that the President of the UK is. The thought is that we can only refer to things that are, even if the things we refer to do not exist.

But this line of thought can be resisted, and even in a fairly convincing way, as the famous 20th century philosopher and Nobel laureate Bertrand Russell has showed. The sentence “The President of the UK doesn’t exist” should not be thought to refer to anything at all—and certainly not to a non-existing head of a non-existing republic. Why not? Because that sentence can be paraphrased into an equivalent sentence (one with exactly the same meaning) that does not even seem to carry the entailment that there is something that doesn’t exist. The paraphrase is this: “Nothing is the President of the UK”. Or, formulated in the way suggested by Frege: “The number of things that is the President of the UK is zero”. These sentences are equivalent to the sentence we started with, but do not suggest that the President of the UK, somehow, is.

Another argument that has led some philosophers to believe there is a distinction between being and existence (and hence that there are things that do not exist) has to do with intentionality. Intentionality, Franz Brentano famously said, is “the mark of the mental”. By this he meant that when we think, we think about something—our thinking is, when we think, directed to an object. When we think about the Swiss mountains, or think that 5+7=12, our thoughts are directed to the Swiss mountains and a particular sum respectively. But now note that it is possible to think about things that do not exist. You can think about the sister you never had, or about Scrooge and Marley –two character in Charles Dickens’ A Christmas Carol in Prose—none of who exist. But they are there for you to think about nonetheless.

This line of thought too can be resisted. One could, for example, think that it is just wrong to say that each and every thought has an object. Some thoughts have objects, for example your thoughts about the Swiss mountains, and your thoughts about the Eiffel tower. But not all thoughts have objects—for instance your thoughts about the sister you never had, and about Scrooge and Marley. They are as little directed at something as an archer’s arrow is directed at something when the archer, mistakenly, takes a cloud formation for a dove.

There is, however, something unsatisfactory about this response. For it seems that your thoughts are really about something, and that they do have objects when you think about the sister you never had, and about Scrooge and Marley. To be sure, the sister you never had is not a person of flesh and blood, someone who breathes and eats, someone who has thoughts and feelings. There is no person of flesh and blood who is the sister you never had. The number of persons that are the sister you never had is zero. But nonetheless—there is the fantasy image of the sister you never had. And that fantasy image does exist and it is the object of your thoughts when you think about the sister you never had. The same can be said about Scrooge and Marley: there are no persons of flesh and blood that are Scrooge and Marley, but there are fictional characters that are Scrooge and Marley. And fictional characters exist, just as the person of flesh and blood who is your neighbor exists. When you think about Scrooge and Marley, the object of your thoughts is not persons of flesh and blood, but fictional characters.

If this line of reasoning is correct, then we should conclude that the arguments for distinguishing between being and existence fail, and that as yet we have seen no reason for making this distinction. (And we should also note that in ordinary language we just use “being” and “ existing” as synonyms). But this line of reasoning does give rise to a new question:

5 • Has ‘exist’ multiple senses or one?

This question arises, for you may think (and I have heard it said many times) that in the following sentences the word “exist” and its synonyms and derivations have different senses:

  1. Stones exist

  2. Cells exist

  3. There are cows in the meadow

  4. There are hotels in Paris

  5. There is a prime number between 4 and 6

  6. God exists

  7. There is a principle that says that if two things are equal to a third thing, they are equal to each other

  8. There is such a thing as the virtue of fidelity

You may think that when we say about stones that they exist, we say something different about them than when we say about cells that they exist. Likewise, you may think that for cows to exist is something different than what it is for hotels in Paris to exist. And again, you may think that what it is for a prime number or a principle to exist is very different than what it is for a virtue or for God to exist. Your question is, thus, whether in each of these statements the word “exist” is used in the same sense. Or, to put the same question in yet another way, your question is whether “exists” in all these sentences is used univocally (i.e. in the same sense), or analogically (i.e. in somewhat related senses) or equivocally (i.e. in unrelated senses).

One possible answer, one that appeals mostly to philosophers in the continental- existentialist tradition (see Corijn van Mazijk’s chapter on “Examining Life”), has it that in the eight sentences on the list “exist” is used in different, though perhaps related senses—but surely not univocally, not in the same sense. These philosophers are attracted to the notion of “ways of being” and they like to say that stones and cells, cows and hotels, numbers, principles and God all have their own, and possibly unique, “way of being”, that they “exist” in different ways, and hence that “exist”, when said of the items on the list, is used in analogical senses. It is incumbent upon philosophers who think this way to explain what these analogically related senses of “exists” are. And when they seriously try to do so, they will have to say such things as: “well, stones are lifeless but cells are alive—hence stones exist in another way, have another ‘mode of being’, than cells. And cows are concrete, while numbers are abstract—hence, cows exist in another way that numbers, they have different ‘modes of being’. And so on for the other items on the list.” There is reason to think, however, that this line of thought is not the best one to have. For there is an elegant alternative: all the items on the list, assuming (if only for the sake of argument) that they are real, are items with radically different natures. Let us say that two things are of a different nature if the set of essential properties that one of the things has is not identical to the set of essential properties that the other thing has. And a property is an essential property of a thing, provided the following is the case: if the thing would lose that property, it would stop being that thing. For example: being odd is an essential property of the number 9—it is a property that the number 9 could not lose without stopping to be that number. Also, being a person is an essential property of you reader—it is a property that you have, and continue to have through all the changes you have gone through. Loss of that property would mean the termination of your existence. Now, a stone has a nature that differs from that of a cell, because the set of essential properties of a cell includes the property of being capable of replication—which is not an element in the set of essential properties of a stone. And so it goes for all the items on the list: I selected them because each has a nature that differs from the nature of all the other items on the list. So, the list refers to items with radically different natures. Now we know that things of different natures exist: we know, for example, that stones exist and we also know that cells exist etc. But if all of these things, with their different natures, exist, they exist in the one and only sense that the word “exist” has. So, on this view, the word “exist” (and its synonyms and derivates) is used univocally throughout the list.

Why should we prefer the latter view? I offer two reasons. First, whereas the first makes use of one unclear notion of “mode or way of being”, the second uses two intuitively very clear notions, viz. (an item’s) “nature”, and (that item’s) “existence”. And it is much better to work with two clear notions than with one unclear one. Second, it is often said that there are close structural parallels between (what we can say about) the notion of “existence” and the notion of “truth”. There is one notion of truth—and the traditional way to unpack it is by saying that a statement is true, if and only if what the statement says to be the case, actually is the case. Nothing more is needed and nothing less will suffice. The statements “stones do not reproduce themselves” and “cells reproduce themselves” are both true, even though the first statement states a physical fact and the second a biological fact—and physical facts and biological facts have very different natures. Yet, both statements are true in the one sense that “true” has. This is analogous to saying that stones and cells exist in the one sense that “exist” has, even though stones and cells have radically different natures.

6 • The existence of universals

So far this chapter dealt with “meta-ontological” matters. We now consider two “ground-level” ontological questions. We can enter the first by reflecting on the following fact: there are yellow flowers, yellow clothes, and chicken egg’s yolks are yellow too. We can state this fact by saying that there is a property, viz. being yellow, that is a property of many flowers, of many clothes, and of all chicken egg yolks. Also, Oslo is north of Amsterdam, Belo Horizonte is north of Rio de Janeiro, and Vladivostok is north of Pusan. We can state this fact by saying that there is a relation, viz. the “is north of”-relation, in which these ordered pairs of cities stand. Similarly, your neighbour is a human being, your aunt Elizabeth is a human being, and the King of Belgium is a human being. We can state this fact by saying that there is a kind, viz. the kind “human being” to which all three persons belong.

These statements may sound unremarkable, but there is something truly amazing about them. For they say that there are properties, that there are relations, and that there are kinds. And this, as was suggested before, is equivalent to saying that properties, relations, and kinds exist. What is amazing about this is that while many people, when asked to give an inventory of what exists, will say “Well, there are inanimate things like rocks; there are living things like gazelles; there are soccer clubs like Tottenham Hotspur; there are banks like the Royal Bank of Scotland”, but few will add “and there are properties, relations, and kinds”. What is also amazing is that, if properties, relations and kinds truly exist, numerically different things can have the very same property—which means that one the same thing (property, relation, kind) can be present at different locations, and at different times.

The things that have the properties, and stand in relations or that belong to kinds are usually called particulars. This contrasts with the properties themselves. Relations and kinds that are called universals as they are shared by numerically distinct particulars. Since properties, relations, and kinds exist, all of which are universals, it follows that universals exist. Or so the so-called ‘metaphysical realist’ holds. Universals, unlike particulars, are ‘repeatable’ entities. In the technical terminology that is often used, universals are ‘instantiated in’ particulars, and also: particulars ‘exemplify’ universals (and particulars ‘belong’ to kinds).

Universals are, moreover, deemed ‘abstract’, by which the realist means that they have no location in spacetime. Universals are often also held to exist even when they are not instantiated in any particular (or even if there is no particular that “belongs” to a kind). An example that may illustrate this idea is the property- universal of being a Dutch female prime-minister. This property, so far, is uninstantiated. But it exists. Similarly for relations and kinds.

Nominalists disagree with all of this. They hold that only concrete particulars exist and deny the existence of universals. So they hold that the yellow of this flower is different from the yellow of the egg yolk. They likewise hold that the “being north of” relation between Oslo and Amsterdam is different from the one between Belo Horizonte and Rio de Janeiro. Again, they hold that your neighbour and your aunt Elizabeth don’t really belong to the same kind (i.e. the kind “human being”) as there are no kinds. Rather, nominalists say, the yellow of the flower and the yellow of the yoke resemble each other, the spatial relation between Oslo and Amsterdam resembles that between Belo Horizonte and Rio de Janeiro, and your neighbour and your aunt resemble each other in various respects. This way of stating the nominalist view is not without problems, as it involves a universal itself—the universal of “resembling”. But nominalists have responses to this that are worth while studying.

7 • Why is there anything at all (and not nothing)?

Let us now move to perhaps the most baffling of all ontological questions. We know that cells and horses exist, and also that mountains, persons, societies, the Earth, the solar system, and the universe exist. And once we start thinking about the fact that all these things exist, it may strike us in a forceful way. Isn’t it incredibly strange, even mysterious, that there are things at all? Wasn’t it possible that the number of things was zero, that there was nothing, really nothing, not even a vast empty space? The philosopher Leibniz therefore urged us to address the question “Why is there something, and not nothing?”3 which is a request for an explanation of the fact that there exists anything at all (so his question is not why horses exist, or mountains, or the Earth, etc.).

There is something remarkable about this question that we must note before we can consider possible answers. Normally when we explain the existence of a particular kind of things, we refer to things that are not of that kind. For example, when we want to explain why there is life on Earth, we refer to the situation in which there was Earth, but no life on it yet, and we point to factors in that situation that led to the emergence of life on Earth. More generally, we normally heed the following Explanatory Principle: for the explanation of the existence of Fs we refer to things that are not Fs but that can held to be causally responsible for Fs coming to be.

If we return to Leibniz’s question, and try to apply the Explanatory Principle, we seem to get stuck. For if we want to explain why there is anything at all (and not nothing), the principle dictates that we refer to what is not anything, i.e. to what is not something—which means that it dictates that it refers to nothing. But nothing is nothing. Nothing is not something—hence not something with properties to which we can refer when we try to explain why there is anything at all. This goes to show that there is something rather strange about Leibniz’ question: it cannot be answered in a way that conforms to the Explanatory Principle.

For this reason some have thought there is something wrong with the question, and hence that we should not even attempt to answer it. The wrongness might be thought to exist in this: ‘explanation’ is a term that makes sense in very specific contexts, e.g. the contexts in which we ask what explains this or that particular phenomenon. But outside such very specific contexts, asking for explanations makes no sense. Still, to many the question “Why is there anything at all?” makes sense, and they have to work towards an answer without wielding the Explanatory Principle. Let us consider a few attempts.

One answer that may come to mind is that God’s existence explains why there is anything at all, God being the creator of all that is. But this answer won’t do. For Leibniz’s question is why there is anything at all and thus demands an explanation of God’s existence (if God exists) as well. This answer leaves God’s existence (if God exists) unexplained.

Another answer that has come to many minds is that the fact that there is anything at all is due to chance, or more sophisticated: it is due to wholly indeterministic ‘quantum fluctuations’. But this won’t do either. For chance is a property of events, and hence there must be events if there is to be chance. But the existence of events is thus left unexplained. Likewise for quantum fluctuations: if quantum fluctuations have led to the existence of anything at all, they must have been there, and hence their existence is left unexplained.

Let us consider three possible answers that don’t seem to suffer from the problem that they leave something unexplained. The first one traces back to St. Anselm, and involves the notion of necessary existence. According to this line of thinking, some things that exist could have not existed—their existence is not necessary but contingent. Examples of contingently existing things include the Eiffel Tower, you and me, and the Kingdom of Sweden. The Eiffel Tower doesn’t exist necessarily—it could never have been built, and so, mutatis mutandis for the other items. Contingently existing things contrast with necessarily existing things. Something O exists necessarily provided it is not possible for O not to exist. If O exists necessarily, then nothing whatsoever can, so to say, push O out of existence.

Now think back to Leibniz’s question, why is there anything at all (and not nothing), and keep in mind the notion of necessary existence. Then we can see that the following is at least an intelligible answer to the question: there are things (and there are not no things) because there is something that exists necessarily and this necessarily existing thing, somehow, explains the existence of contingent things. So, why is there something and not nothing? Because there is something that exists necessarily. These thoughts form the backbone of the so-called ‘modal ontological argument’ (‘modal’ because the argument contains the modal notions of possibility and necessity) inaugurated by the philosopher Norman Malcolm.

In the Western philosophical tradition this necessarily existing thing was often identified with the Christian God. But this requires thorough argumentation—and it is not necessary to make the identification in order to present the conclusion of the modal ontological argument (“There is something that exists necessarily”) as at least an intelligible answer to Leibniz’s question.

A second answer to Leibniz’s question that may not suffer from the “unexplained rest” problem goes by the name of the “axiarchic view”. The train of thought here is that of all the countless ways that the whole of reality could have been, one is the best. And it next suggests that reality as it is, is that best of all possible worlds (to use another famous diction of Leibniz: the actual world is the best of possible worlds). The final part of the train consists in suggesting that it is no accident that the actual world is the best possible world. The actual world, so the suggestion goes, is actual because it is the best.

Friends of the axiarchic view (John Leslie, for example), inevitably, face problems. One problem for them is that the view offers an explanation that is so utterly different in kind from other explanations that we accept and love—like the explanation of why iron expands when heated. But then again, any answer to Leibniz’ question will contain elements that are utterly different from what we find in other explanations that we accept and love.

This holds true for a third response to Leibniz question as well. This response says that the fact that there exists anything at all, is a brute fact, so a fact that defies explanation of any sort. Brute facts are facts for the obtaining of which there is no reason; there is no reason why the fact obtains as little as there would be a reason if the fact would not obtain. This is a response, not an answer to Leibniz’ question. The response is an acknowledgement of the fact that the human intellect is running out of its depths here, and that we must, perhaps grudgingly, accept that existence is an impenetrable mystery.

Again, many, notably friends of scientism, do not like this response. They hold, very roughly, that if science cannot answer a question, there must be something wrong with it. But then again, scientism itself is of questionable reputation.

The American philosopher Robert Nozick once said that Leibniz’ “question cuts so deep ... that any approach that stands a chance of yielding an answer will look extremely weird. Someone who proposes a non-strange answer shows he didn’t understand the question. Since the question is not to be rejected, though, we must be prepared to accept strangeness or apparent craziness in a theory that answers it.”4 I think this is well put.

8 • Envoi

In this chapter, then, I have discussed a number of (as we can now see: interrelated) meta-ontological questions: Is there a property that everything that exists has? Is existence a property? Are being and existence synonyms? Are there things that don’t exist? Next we discussed, however quickly, two ontological questions: Do properties, relations, and kinds exist? and Why is there anything at all? These are some of the main questions that are being discussed within the branch of metaphysics called ontology.

Can we see or expect new developments—either new questions, or new approaches? With all the provisos one should make here, I think we should expect ontological discussion to turn to the following questions: “What is the ontological status of the internet and of virtual reality”? (see the chapter on the philosophy of technology) “What is the ontological status of persons?” “What is the ontological status of race, of gender as well as of ‘nation’?” (see the chapter on political philosophy), and “What is the ontological status of values?”(see the chapter on meta-ethics.) By questions about the “ontological status” of something X, I mean questions about whether or not X exists, of what metaphysical nature X is (if any), whether or not X can be “reduced” to other items that are supposed to exist, and whether or not X is a mere illusion. As to new approaches I see and expect a further development of views according to which the ontological question (so the question: what exists?) should be answered by reference to natural science alone, with a special place reserved for evolutionary theory. I also expect a further development of what are called “scientistic” ontologies. I expect moreover the further development of explicitly feminist approaches to ontological questions. Finally, I expect the continued discussion of Leibniz’s question by science-inspired means and concepts, such as the multiverse theories and structuralism.


Armstrong, D. (1989). Universals. An opiniated introduction. Westview Press.

Aune, B. (1985). Metaphysics. The Elements. University of Minneapolis Press.

Chalmers, D. J., Manley, D., & Wasserman, R. (Eds.). (2009). Metametaphysics: New essays on the foundations of ontology. Clarendon Press ; Oxford University Press.

de Ridder, J., Peels, R., & van Woudenberg, R. (Eds.). (2018). Scientism (Vol. 1). Oxford University Press.

Leibniz, G. W. F. (1971). The monadology and other philosophical writings (R. Latta, Trans.). Clarendon Press,.

Lewis, D. (1999). Papers in metaphysics and epistemology. Cambridge University Press.

Loux, M., & Thomas, M. (2017). Metaphysics. A Contemporary Introduction (4th ed.). Routledge. 10.4324/9781315637242

Lowe, E. J. (2002). A survey of metaphysics. Oxford University Press.

Nozick, R. (1990). Philosophical explanations. Routledge. (Original work published 1981)

Plantinga, A. (n.d.). The ontological argument, from st. Anselm to contemporary philosophers.

Van Inwagen, P. (2014). Existence. Essays in Ontology. Cambridge University Press.

Van Inwagen, P., & Zimmerman, D. W. (Eds.). (2008). Metaphysics: The big questions (2nd, rev.expanded ed ed.). Blackwell Pub.

No comments here
Why not start the discussion?