Abstract
We naturally think of the material world as being populated by a large number of individuals. These are things, such as my laptop and the particles that compose it, that we describe as being propertied and related in various ways when we describe the material world around us. In this paper I argue that, fundamentally speaking at least, there are no such things as material individuals. I then propose and defend an individualless view of the material world I call “generalism”.
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Notes
Individualism is perhaps the most natural view about the structure of our world and is implicit in a large amount of contemporary philosophy. Any metaphysician who describes the fundamental structure of the world by describing what individuals there are and what they are like is, at least implicitly, an individualist. For example, see Lewis (1986). More explicit endorsements of individualism can be found in Wittgenstein (1933) and Russell (1985); and, more recently, in Allaire (1963), Armstrong (1997), and Hawthorne and Sider (2002). Note that the individualist need not claim that all individuals are fundamental entities: she may think, for example, that chairs and tables are nothing other than collections of electrons and quarks.
Readers familiar with the substantivalism/relationalism debate should note that I allow “reference points” to include unoccupied inertial trajectories in substantival spacetime.
I am slurring over a subtlety here. The laws of NGT as written down by Newton himself make reference to absolute velocity, so what Newton wrote down would not be true if there were no such thing as absolute velocity. But I am using the phrase ‘laws of NGT’ to refer to laws that can be expressed in different ways depending on what one takes to be the underlying metaphysics of the world they govern. We use ‘the Schrodinger equation’ in quantum mechanics the same way, to refer to a law that will be formulated in very different ways depending on one’s view about the fundamental ontology of a quantum mechanical world. The claim in the text, then, is that orthodoxy considers a theory that dispenses with absolute velocity and formulates Newton’s laws without reference to it better than Newton’s own theory.
This slurs over some subtleties. First, the term ‘closed systems’ is used as a dummyterm. The reader can think of closed systems as possible worlds, or as mathematical models, or as idealized laboratories with walls that “insulate” against effects from outside. Second, I leave open whether the “initial time” refers to an instant or a (perhaps infintesimally small) period of time. Incidentally, some theorists describe the indented claim as the fact that NGT is “symmetric under uniform velocity boosts” (see for example Wigner 1967). More contemporary formulations of ‘symmetry’ are somewhat different and avoid the complications just mentioned, but the formulation in the text is more intuitive and will suffice for our purposes here.
I believe that this form of argument has been extremely influential throughout the history of physics. For example, when formulating his Special Theory of Relativity, I would argue that Einstein was guided (in part) by the constraint that the correct laws of physics must imply, through reasoning much like that rehearsed, that absolute velocity is empirically undetectable. Admittedly, there is much more to say about what empirical undetectability really amounts to, but a full discussion of the issues involved would take us too far from the main thread of the current paper so I will use the rough characterization in the text for simplicity. I say more about what empirical detectability amounts to in my Symmetry and the Undetectable, in preparation.
Earman (2002, pp. 6–7) discusses the possibility of laws of this type. Aristotle’s physics might be thought of as a theory of this sort: he thought that the universe had a distinguished center, with earth gravitating towards it and fire away from it.
This statement of redundancy assumes that the laws are deterministic. The generalization to probabilistic laws is reasonably straightforward, but considerations of space prevent me from discussing it here.
Russell (1948a, 1948b, p. 97) respectively. Other proponents of this tradition include Locke, who described primitive individuals as an ‘unknown support of those qualities’ (see Locke 1997, II xxiii 2); and Hume, who described them as ‘unknown and invisible’ (see Hume 1978, p. 220). I should say that none of these authors called their subject matter “primitive individuals”, but I believe they were all talking about them.
Not all philosophers would agree with the way I put things here. For example, Campbell (2002) defends a view on which the phenomenal character of an experience depends on which individual one is presented with, and he may therefore want to say that the two situations would look different. Nonetheless, he can agree that there is a sense in which the two situations are indistinguishable and that we cannot tell the difference between them. This is, strictly speaking, all my arguments require, but for ease of prose I shall sometimes slur over this subtlety and talk of the situations as looking the same.
See Strawson (1959, pp. 15–38) for a discussion of the importance of these everyday senses of ‘knowing what’.
One might argue that the same remarks apply to the case of velocity. Suppose you said to yourself ‘I hereby let “Bob” name the real number that is my absolute velocity in miles per hour’, and then thought my velocity through space is Bob miles per hour. Now, it is debatable whether this would really result in a similar type of knowledge as that just outlined in the case of individuals. But even if we grant that it would, it remains the case that scenarios differing only in facts about absolute velocity would be indistinguishable to you, and so it would remain the case that absolute velocity is empirically undetectable in our sense.
I try to say some of it in Dasgupta, Symmetry and the Undetectable, in preparation.
Hawthorne and Sider (2002) develop the view in more detail than most; however, the view they emerge with (though do not endorse) has more in common with the theory I develop in the next section.
I should say that the title ‘Identity of Indiscernibles’ is sometimes used to name other related principles, but the details of these other principles need not concern us here.
It is uncontroversial that the bundle theory implies IOI. What is controversial is whether this counts against the view. See Hacking (1975) and O’LearyHawthorne (1995) for arguments that it does not. I should say that some theorists appear to deny that the bundle theory implies IOI (for example, RodriguezPereyra 2004), but on closer examination it invariably turns out that they are referring to views that identify individuals with bundles of propertyinstances or tropes. For the reasons just given in the text, this is not the sort of view under consideration here.
Just to clarify, my objection to the bundle theory is not that it implies IOI and we have apriori reasons to think that there are possible worlds that are counterexamples to IOI. Others object to the bundle theory in this way, but as I said in the introduction I wish to bracket apriori intuitions about what worlds are possible. Instead, my objection is that the bundle theory implies IOI and IOI is utterly unmotivated by my arguments against primitive individuals.
It may be interesting to note that in his seminal paper on this topic, Adams (1979) claims that the denial of primitive individuals ‘stands or falls… with a certain doctrine of the Identity of Indiscernibles’ (p. 11). I believe he said this because he fell into the same trap as the bundle theorist, namely of asking what individuals are, if not primitive entities. I hope to show here that another approach is possible.
Lewis calls this view ‘antihaecceitism’, and uses ‘haecceitism’ to label the view that there are purely individualistic differences between some possible worlds (Lewis 1986, p. 221). This terminology is the norm in one wing of the literature, but I hesitate to use it because other wings of the literature use this terminology to denote different distinctions.
This may have been the view discussed (though not endorsed) by O’LearyHawthorne and Cover (1996), when they write that a theorist ‘may insist that the full story about that world [can] be captured by general propositions, of the sort \((\exists\hbox{x})(\hbox{x is a sphere}), (\exists \hbox{x})(\exists \hbox{y})(\hbox{x is a sphere and y is a sphere and x }\neq \hbox{y})\), and so on.’ (p. 12). In this quotation they are talking about a possible world, but the analogous view about the actual world sounds very close to the view under consideration.
I am not aware of a view like generalism being proposed in the literature. The closest I have come across is a view discussed very briefly by Van Cleve in the last section of his (1985). It also bears some similarity with the ‘ontological nihilism’ of Hawthorne and Cortens (1995). The language G described here is borrowed from a language discussed by Quine (1976) and developed by Kuhn (1983). Burgess and Rosen (1997) discuss the prospects of using a language like this to pursue nominalism in the philosophy of mathematics, but the literature contains little discussion of the prospects of using it to formulate a generalist metaphysics.
I should also say that the ontology will include properties of adicity zero which might more accurately be called ‘states of affairs’, but I will discuss this in more detail later on.
For ease of prose I will be rather sloppy about the usemention distinction in what follows. I do not think this will lead to any serious confusion.
Incidentally, she expresses (A) with the sentence \({\user2{cc}}{\bf (}{\user2{F}}^{\bf 1}\,{\boldsymbol{\&}}\,{\user2 {pF}}^{\bf 1}\,{\boldsymbol{\&\,\sim}}{\user2{I}}{\bf )}{\user2{obtains}}.\)
This is not to say that the generalist dispenses with danglers all together, for she may think that there is such a thing as absolute velocity! But the point is that she goes some way towards a danglerless worldview by dispensing with primitive individuals.
Russell (1985) was, of course, the classic atomist.
For those readers familiar with G, the generalist will really state this as the fact that \({\user2{cc}}{\bf (}{\user2{F}}^{\bf 1}\, {\boldsymbol{\&}}\, {\user2{pG}}^{\bf 1}\,{\boldsymbol{\&}}\,{\user2{R}}^{\bf 2}\,{\boldsymbol{\&}\,\boldsymbol{\sim}}{\user2{I}}^{\bf 2}{\bf )}\,{\user2{obtains}}.\)
In G we would express these as the facts that \({\user2{cF}}^{\bf 1}\,{\user2{obtains}},\) that \({\user2{cG}}^{\bf 1}\,{\user2{obtains}},\) and that \({\user2{ccR}}^{\bf 2}\,{\user2{obtains}}.\)
Schaffer (2007) has recently discussed a view he calls ‘Monism’. On this view there is just one individual, the “world object”; or, at least, if there are other individuals they are to be thought of as derivative from the world object, which is the fundamental entity. Generalism and monism share some similarities, but notice that monism is, at least on the face of it, atomistic: the entire situation concerning the world object can be decomposed into the fact that it is F, the fact that it is G, and so on.
Laplace, Exposition du System du Monde, quoted in Gribbin (2002, p. 298).
See Hawthorne and Sider (2002).
A precise characterization of “local causation” would require much more finetuning, but this will do for our purposes.
I am slurring over some subtleties here. For one thing, there might be ‘identifying descriptions’ that would make her life easier. But there is little reason to think that such descriptions will be available in general. And in any case that method of information storage is extremely impractical: if our agent were to discover that part of the identifying description is false she would have to revise every single belief about the thing she thinks satisfies the description!
I should emphasize that the above story is not about the semantics of constants in our agent’s language of thought. The claim is just that the pragmatic usefulness of constants explains why they exist in her mental language in the first place.
One could expand G to include sentential connectives, variables and quantifiers ranging over properties, modal operators and so on, but I shall not explore these expansions here.
The following semantics is borrowed from Kuhn (1983).
Roughly speaking, we say that the formula is true on the model if and only if it is satisfied by every sequence in the model. To define the notion of a formula being satisfied by a sequence in the model, we need a way to associate free variables in the formula with objects in the sequence. Here we can simply use the convention that the i’th free variable is associated with the i’th object in the sequence.
To prove these, define translation functions from nary formulas of predicate logic to nplace predicates of Q and vice versa, and then prove that the value of each function is always equivalent to the argument. For one example of translation functions like this see Kuhn (1983).
References
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Acknowledgements
Thanks to Kit Fine for extensive discussions on these topics. Thanks also to David Brian Barnett, Ned Block, Jonny Cottrell, Hartry Field, Paul Horwich, Geoff Lee, Farid Masrour, John Morrison, Karl Schafer, Jonathan Schaffer, Stephen Schiffer, Michael Schweiger, Ted Sider, Peter Unger, Seth Yalcin, and participants of the NYU dissertation seminar during the spring of 2008 for extremely helpful comments on earlier drafts of this paper.
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Appendix on language G
Appendix on language G
First I will define the syntax of language G and give a more complete and precise explanation of what the termfunctors mean. Then I will define a notion of logical implication on G and a relation of equivalence between G and PL. Third, I will outline the proof that the relation of equivalence satisfies Sufficiency, Modesty, and Preservation, as required. Finally, I will respond to an objection to the way these tasks are carried out.
1.1 The syntax of G
The vocabulary of G consists of a countable set of atomic terms, each associated with an integer n ≥ 0, including a term \({\user2{I}}^{\bf 2}\) associated with the number 2. If a term of G is associated with the integer n, we call it an nplace term. The vocabulary of G also includes six termfunctors \({\boldsymbol{\&},\,\boldsymbol{\sim,}}\, {\user2{c},\,\user2{p}},\, {\boldsymbol{\imath}},\,\hbox{and}\,{\boldsymbol{\sigma}}\). The set of terms are then defined inductively as follows:

1.
All atomic nplace terms are nplace terms.

2.
If \({\user2{P}}^{\user2{n}} \hbox{ and } {\user2{Q}}^{\user2{m}}\) are nplace and mplace terms respectively, then

(a)
\({\boldsymbol{\sim}} {\user2{P}}^{\user2{n}},\, {\boldsymbol{\imath}}{\user2{P}}^{\user2{n}},\,\hbox{and}\,{\boldsymbol{\sigma}}{\user2{P}}^{\user2{n}}\) are nplace terms,

(b)
\({\user2{cP}}^{\user2{n}}\) is an (n − 1)place term unless n = 0, in which case it is a 0place term.

(c)
\({\user2{pP}}^{\user2{n}}\) is an (n + 1)place term, and

(d)
\({\bf (}{\user2{P}}^{\user2{n}}\,\boldsymbol{\&}\,{\user2{Q}}^{\user2{m}}{\bf )}\) is a max(n, m)place term.

(a)

3.
That’s all; nothing else is a term.
Finally, the vocabulary of G includes a single predicate, \({\user2{x\,obtains}}.\) A sentence of G is an expression of the form \({\user2{P}}^{\bf 0}\,{\user2{obtains}},\,\hbox{ where }\,{\user2{P}}^{\bf 0}\) is a 0place term.^{Footnote 40}
1.2 The termfunctors
In the text I gave a partial explanation of what the termfunctors mean by saying things like ‘if \({\user2{L}}^{\bf 2}\) is the 2place property of loving, which we ordinarily understand as holding between individuals x and y if and only if x loves y, then \( {\bf (}{\user2{L}}^{\bf 2}\,{\boldsymbol{\&}\,\boldsymbol{\sim}\boldsymbol{\sigma}}{\user2{L}}^{\bf 2}{\bf )}\) is the 2place property of loving unrequitedly, which we ordinarily understand to hold between individuals x and y if and only if x loves y and y does not love x.’
Here I shall give a more precise and general explanation of what the termfunctors mean in this form. But there are two points worth keeping in mind. First, I am explaining what the termfunctors mean in terms that we ordinarily understand, namely in terms of individuals. But of course this is just an explanatory convenience, and we should keep in mind that the properties are ultimately to be understood independently of a domain of individuals. For a discussion of the legitimacy of this explanatory technique, see the end of this appendix. The second thing to keep in mind is that in the above quotation from the text the ‘if and only if’ is not a material biconditional—if it were, it would not allow me to pick out the intended properties. I shall not discuss exactly what biconditional it is, but I take it that we understand the quotation above well enough to be getting on with.
Now for the explanation of the term functors. Let \({\user2{P}}^{\user2{n}}\) be the nplace property we ordinarily understand as holding of individuals x _{1}…x _{ n } if and only if ϕ(x _{1}…x _{ n }). And let \({\user2{Q}}^{\user2{m}}\) be the mplace property we ordinarily understand as holding of individuals y _{1}…y _{ m } if and only if ψ(y _{1}…y _{ m }). Then

1.
\({\boldsymbol{\sim}}{\user2{P}}^{\user2{n}}\) is the nplace property we ordinarily understand as holding of x_{1}…x_{ n } if and only if it is not the case that ϕ(x_{1}…x_{ n });

2.
\({\bf (}{\user2{P}}^{\user2{n}}\,{\boldsymbol{\&}}\,{\user2{Q}}^{\user2{m}}{\bf )}\) is the max(n, m)place property that we ordinarily understand as holding of x_{1}…x_{ k } if and only if ϕ(x_{1}…x_{ n }) and ψ(x_{1}…x_{ m }), where k = max(n, m);

3.
\({\boldsymbol{\sigma}} {\user2{P}}^{\user2{n}}\) is the nplace property we ordinarily understand as holding of x_{1}…x_{ n } if and only if ϕ(x_{ n }x_{1}x_{2}…x_{n1});

4.
\({\boldsymbol{\imath}} {\user2{P}}^{\user2{n}}\) is the nplace property we ordinarily understand as holding of x_{1}…x_{ n } if and only if ϕ(x_{2}x_{1}x_{3}…x_{ n });

5.
If n ≥ 1, then \({\user2{cP}}^{\user2{n}}\) is the (n − 1)place property that we ordinarily understand as holding of x _{2}…x _{ n } if and only if there is something x _{1} such that ϕ(x_{1}…x _{ n }); otherwise \({\user2{cP}}^{\user2{n}}\) is the 0place property \({\user2{P}}^{\user2{n}};\)

6.
\({\user2{pP}}^{\user2{n}}\) is the (n + 1)place property that we ordinarily understand as holding of x_{1}…x_{n+1} if and only if ϕ(x_{2}…x_{ n }x_{n+1}).
Finally, \({\user2{I}}^{\bf 2}\) is identity, the 2place property we ordinarily understand as holding between x and y if and only if x is identical to y.
1.3 Predicate functor logic
Our task now is to define a relation of logical consequence on G and a relation of equivalence between G and PL in such a way that we can prove Sufficiency, Modesty, and Preservation. We shall reduce this task to one already accomplished by defining a closely related language of “predicate functor logic” I will call Q.^{Footnote 41} There is already a welldefined relation of consequence on Q and a relation of equivalence between Q and PL for which analogues of these three theorems hold, and we will use this fact to induce corresponding relations on G and prove our theorems.
Syntactically speaking, the language Q is just the same as G with the exception that (i) it does not contain G’s single predicate \({\user2{x\,obtains}},\) and (ii) its expressions are written in normal font rather than the bold font of G. The terms in G are, when written in the normal font of Q, to be understood as predicates instead. More precisely, the vocabulary of Q consists of a countable set of atomic nplace predicates, including a 2place predicate I ^{2}, and six predicate functors ∼, &, c, p, \(\imath\,\hbox{and}\,\sigma.\) An expression of the form P ^{n} is an atomic nplace predicate of Q if and only if \({\user2{P}}^{\user2{n}}\) is an atomic nplace term of G; an expression of the form ∼P ^{n} is an nplace predicate of Q if and only if \({\boldsymbol{\sim}}{\user2{P}}^{\user2{n}}\) is an nplace term of G; and so on.
We can define a notion of logical implication on Q modeltheoretically. Without loss of generality, we can assume that the predicates of Q are the predicates of PL. So we can give a semantics for Q using the standard models of PL (i.e. predicate logic with identity but without constants).^{Footnote 42} These models are pairs of the form M = (D, v), where D is a nonempty set and v is a function from nplace predicates (other than I^{2}) to sets of ntuples of D. Given a predicate P ^{n} of Q, a model M = (D,v) and a sequence d = (d _{1}, d _{2}…) of elements of D, we say that d satisfies P ^{n} in M, written d⊧_{ M } P ^{n}, if and only if

1.
If P ^{n} is atomic then \((d_1,\ldots, d_n) \in v(P^n)\),

2.
If P ^{n} = I ^{2} then d _{1} = d _{2},

3.
If P ^{n} = ∼ Q ^{n} then it is not the case that \(d \models_M Q^n\),

4.
If \(P^{n}=(Q^m\,\&\,R^r)\) then \(d\models_M Q^m\) and \(d\models_M R^r\),

5.
If P ^{n} = c Q ^{n+1} then there is an \(x \in D\) such that (\(x, d_1, d_2, \ldots)\models_M Q^{n+1}\),

6.
If P ^{n} = p Q ^{n−1} then (\(d_2, d_3, \ldots)\models_M Q^{n1}\),

7.
If \(P^{n}=\imath Q^n\) then (\(d_2, d_1, d_3, d_4, \ldots) \models_M Q^n\), and finally

8.
If \(P^n={\sigma}Q^n\) then (\(d_n, d_1, d_2,\ldots, d_{n1}, d_{n+1}, \ldots)\models_M Q^n\).
We can then say that P ^{n} is true on M, written \(\models_M P^{n}\), if and only if \(d \models_M P^{n}\) for all sequences d = (d _{1}, d _{2},…) of elements of D.
With this semantics in place, it is now easy to define a relation of logical implication on Q and a relation of equivalence between Q and PL. First, the relation of logical implication can be defined as follows: a predicate P ^{n} logically implies a predicate Q^{m}, written P ^{n}⊧ Q ^{m}, if and only if for any model M, if ⊧_{ M } P ^{n} then ⊧_{ M } Q ^{m}.
Now for the relation of equivalence between Q and PL. Remember, the models M = (D, v) are models of PL too. So let us assume that the notion of an nary formula \(\phi(x_1\ldots \,x_n)\) of PL being true on a model M, written \(\models_M \phi(x_1\ldots\, x_n)\), is defined in the normal way.^{Footnote 43} Then we can say that an nary formula \(\phi(x_1\ldots\, x_n)\) of PL and a predicate P ^{n} of Q are equivalent if and only if for every model M, \(\models_M \phi(x_1 \ldots\, x_n)\) if and only if \(\models_M P^{n}\).
For our purposes the important results are these:

QSufficiency Every nary formula of PL is equivalent to some nplace predicate of Q.

QModesty Every nplace predicate of Q is equivalent to some nary formula of PL.^{Footnote 44}
With these results in hand, our task is now easy.
1.4 Implication, equivalence, and our three theorems
First, we use Q to define a relation of consequence on G and a relation of equivalence between G and PL. Then we prove our three theorems.
The relation of logical implication on Q naturally induces a relation \(\preceq\) between terms of G: \({\user2{P}}^{\user2{n}}\preceq {\user2{Q}}^{\user2{m}}\) if and only if \(P^{n}\models Q^m\). In turn, this induces a relation of logical implication on sentences of G: \({\user2{P}}^{\bf 0}\,{\user2{obtains}}\) logically implies \({\user2{Q}}^{\bf 0}\, {\user2{obtains}},\) written \({\user2{P}}^{\bf 0}\, {\user2{obtains}} \models {\user2{Q}}^{\bf 0}\, {\user2{obtains}},\) if and only if \({\user2{P}}^{\bf 0} \preceq {\user2{Q}}^{\bf 0};\) that is, if and only if \(P^{0}\models Q^{0}.\) (The sign ‘\(\models\)’ is being used for logical implication in both languages, but I take it that no confusion will result.)
The relation of equivalence between Q and PL also induces a relation of equivalence between G and PL: a sentence \({\user2{P}}^{\bf 0}\, {\user2{obtains}}\) of G is equivalent to a sentence p of PL if and only if P ^{0} is equivalent to p.
Preservation is now easy to prove. Suppose a sentence \({\user2{P}}^{\bf 0} \,{\user2{obtains}}\) in G is equivalent to a sentence p in PL, and suppose a sentence \({\user2{Q}}^{\bf 0} \,{\user2{obtains}}\) in G is equivalent to q in PL. We must show that \({\user2{P}}^{\bf 0}\,{\user2{obtains}} \models {\user2{Q}}^{\bf 0}\,{\user2{obtains}}\) if and only if \(p \models q.\) Now, \({\user2{P}}^{\bf 0}\,{\user2{obtains}} \models {\user2{Q}}^{\bf 0}\,{\user2{obtains}}\) if and only if \(P^0 \models Q^{0}\) (by definition of implication in G). But P^{0} is equivalent to p and Q^{0} is equivalent to q (by our hypothesis and the definition of equivalence between G and PL), and therefore \(P^{0} \models Q^{0}\) if and only if \(p \models q\) (by modeltheoretic reasoning). So \({\user2{P}}^{\bf 0}\,{\user2{obtains}} \models {\user2{Q}}^{\bf 0}\, {\user2{obtains}}\) if and only if \(p\models q,\) as required.
Finally, Sufficiency and Modesty follow straight from QSufficiency and QModesty along with the above definitions.
1.5 Using a domain of individuals
Earlier in the appendix and in the text I explained what the termfunctors of G mean by appealing to our ordinary understanding of properties being instantiated by a domain of individuals. But the generalist claims that individuals are not constituents of the fundamental facts of the world. So was that method of explanation legitimate?
Similarly, I just used the semantics for Q to define a relation of implication on G and a relation of equivalence between G and PL. But the semantics for Q used ordinary models of PL of the form M = (D, v), where D is a domain of individuals. Was that legitimate?
I think it was. The key is to distinguish between metaphysical and conceptual priority. Metaphysically, the generalist claims that the fundamental facts of the world are those expressed by G. But conceptually, I have explained the view to you in terms that you are familiar with, namely in terms of individuals. Once you are competent with G you can then, if you so wish, become a generalist by giving up your understanding of G in terms of a domain of individuals and simply taking the termfunctors and predicate of G as undefined primitives.
There is no space to defend the cogency of the strategy here in full. I shall only plead innocence by association, for there are many other cases in which we adopt it. The case of velocity is, unsurprisingly, a good example. Our ordinary concept of the relative velocity between two material things is defined as the difference between their absolute velocities. Once you are competent with the concept, you can then (if you so wish) dispense with absolute velocity and either think of relative velocity as a primitive concept or define it in other terms. And this is precisely what we do when we adopt a Galilean conception of spacetime.
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Dasgupta, S. Individuals: an essay in revisionary metaphysics. Philos Stud 145, 35–67 (2009). https://doi.org/10.1007/s110980099390x
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DOI: https://doi.org/10.1007/s110980099390x