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  <front>
    <journal-meta />
    <article-meta>
      <title-group>
        <article-title>The Identity of Property Particulars</article-title>
      </title-group>
      <contrib-group>
        <contrib contrib-type="author">
          <string-name>Claudio MASOLO</string-name>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Adrien BARTON</string-name>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Laboratory for Applied Ontology</string-name>
        </contrib>
        <contrib contrib-type="author">
          <string-name>ISTC-CNR</string-name>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Trento</string-name>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Italy</string-name>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Institut de Recherche en Informatique de Toulouse</string-name>
        </contrib>
        <contrib contrib-type="author">
          <string-name>France</string-name>
        </contrib>
      </contrib-group>
      <abstract>
        <p>A property particular is a particular that characterizes the satisfaction of a property by an object, for example the 'redness' of a specific rose. We consider three theories of identity for property particulars, illustrating them on a common example. We discuss their strengths and weaknesses, and whether they can be interpreted in an epistemic or realist perspective. We introduce some first steps of a theory of reification of property types and discuss the benefits that it could bring.</p>
      </abstract>
      <kwd-group>
        <kwd />
        <kwd>Property</kwd>
        <kwd>identity</kwd>
        <kwd>realism</kwd>
        <kwd>epistemology</kwd>
        <kwd>existential dependence</kwd>
      </kwd-group>
    </article-meta>
  </front>
  <body>
    <sec id="sec-1">
      <title>1. Introduction</title>
      <p>
        Properties are one of the most basic building block of ontologies. A variety of kinds of
properties has been proposed by ontologists: qualities (e.g. the redness of a rose),
realizable entities like dispositions (e.g. the fragility of a glass), functions (e.g. the function
of a heart to pump blood), roles (e.g. a doctor role), etc. Several foundational
ontologies introduce into the domain of quantification the individualization of properties, e.g.,
the redness of a particular rose or the weight of a given car, which are specific of (they
inhere in) the rose and the car, respectively. For instance, BFO [
        <xref ref-type="bibr" rid="ref1">1</xref>
        ] considers dependent
continuants, DOLCE [
        <xref ref-type="bibr" rid="ref2">2</xref>
        ] individual qualities, GFO [
        <xref ref-type="bibr" rid="ref3">3</xref>
        ] property individuals, and UFO [
        <xref ref-type="bibr" rid="ref4">4</xref>
        ]
moments. We focus on individualizations of properties, called here property particulars
(PPs), corresponding to the satisfaction of a property by an object. In a philosophical
perspective, PPs are interpetrable in several ways, e.g., as tropes [
        <xref ref-type="bibr" rid="ref5">5</xref>
        ] or truth-makers [
        <xref ref-type="bibr" rid="ref6">6</xref>
        ], and
they are intertwined with more complex entities like states of affairs [
        <xref ref-type="bibr" rid="ref7">7</xref>
        ] or facts [
        <xref ref-type="bibr" rid="ref8">8</xref>
        ]. The
introduction of PPs into the domain of quantification brings a variety of representational
advantages, such as analyzing the relations between simple PPs and the complex ones
they compose (enabling, for instance, a finer analysis of causality as in [
        <xref ref-type="bibr" rid="ref9">9</xref>
        ]), or modeling
some meta-properties via properties of PPs.
      </p>
      <p>
        However, the identity conditions of PPs have been little studied (but see [
        <xref ref-type="bibr" rid="ref10">10</xref>
        ] for an
investigation into the identity of dispositional properties). This question if deeply
intertwined with the epistemic or realist position one takes to interpret an ontological
framework. Since PPs are intuitively interconnected with propositions, they might be
epistemically interpreted as pieces of information about objects, observations or cognitive
categorizations. A theory could then admit a PP corresponding to the red character of a
rose without introducing a PP corresponding to its specific shade of red, e.g., its specific
scarletness. This would represent the situation where the only information at hand
concerns the fact that the rose is red, and where no information is available about its specific
shade of red. On the other hand, a realist framework might impose that the redness of a
rose would be identical with (or at least would depend on) its scarletness. An important
theoretical work would therefore be to clarify the identity conditions for PPs and their
adequacy to capture a realist vs. epistemic stance.
      </p>
      <p>The question of the identity of PPs is linked with two other questions that are still
matter of debate and that we will not discuss here: first, whether and how PPs can persist
through time; second, which kinds of properties are associated with PPs, and which kinds
are not. Instead, we will analyze identity criteria in a static scenario where a given set of
properties (and associated PP-types, see Sect. 2) are taxonomically organized.</p>
    </sec>
    <sec id="sec-2">
      <title>2. Property Particulars</title>
      <p>Suppose one wants to represent the situation where ‘the object a has the property P’,
shortly, ‘a is P’ or, as usually stated in the philosophical literature, ‘a instantiates P’.
In first order logic (FOL) one would typically represent the object a by the individual
constant a, the property P by the unary predicate P, and the instantiation of the property
P by the object a by the proposition P(a). For example, the property being red would be
represented by a predicate RED, and the red character of a rose r would be represented by
the proposition RED(r).2</p>
      <p>An alternative way to represent (also in FOL) this kind of situations relies on
property particulars. In the above situation, on top of the object a, we have an additional
individual, a PP inhering in a that intuitively stands for ‘a’s being P’. The inherence relation
between PPs and objects, a kind of specific existential dependence, is represented by the
primitive INH that is minimally characterized by axioms (a1)-(a3), where PP(p) stands
for ‘p is a property particular’ and OB(a) for ‘a is an object’. Because a PP always
inheres in a unique object (a2)—but an object may have several PPs inhering in it—we
note pa a PP inhering in a.3
a1 INH(p; a) ! PP(p) ^ OB(a)
a2 INH(p; a) ^ INH(p; b) ! a = b
a3 PP(p) ! 9a(INH(p; a))</p>
      <p>In a framework containing PPs, the property P can be associated with a type of PPs
represented by the predicate P¯. Therefore, ‘a is P’ is represented by 9p(INH(p; a) ^ P¯ (p)).
For instance, the fact that the rose r is red can be represented by 9p(INH(p; r) ^ RE¯ D(p)),
i.e., being red is read as ‘having an inherent RE¯ D-PP’. Given the fact that PPs can be
interpreted in several ways, we introduce P¯ without making any further commitment (e.g.,
theories of tropes usually reduce P¯ to an equivalence class of similar PPs).</p>
      <sec id="sec-2-1">
        <title>2We assume here that the rose r has a uniform color.</title>
        <p>3To improve the readability of formulas we assume the following conventions: (i) individual constants are
noted using the typewriter typestyle font; (ii) variables are noted in italic; (iii) variables/constants ranging
over objects are noted a; b; : : : a; b; : : :; (iv) variables/constants ranging over PPs are noted p; q; : : : ; p; q; : : :</p>
      </sec>
    </sec>
    <sec id="sec-3">
      <title>3. Specialization and Covering</title>
      <p>We consider a scenario where the user (that could have a realist or epistemic stance)
wants to represent the taxonomical organization of a finite set P of properties of objects
using a FOL-framework. We assume that the user commits to the set of properties P and
to their taxonomical organization, and we want to analyze the adequacy of alternative
FOL-frameworks (especially the ones based on PPs) for representing this commitment.
This scenario may be extended to denumerable sets of properties and relations, but here
we stick to the finite case of properties.</p>
      <p>Classically, each property in P would be represented by a unary predicate that
applies to objects. We note P the set of FOL-predicates defined on objects representing the
properties in P . Alternatively, as seen in Sect. 2, properties can be represented by means
of unary predicates that applies to PPs. Calling P¯ the set of FOL-predicates defined on
PPs representing the properties in P , we assume one-to-one mappings between P , P,
and P¯ . Given the property P 2 P , we note P 2 P the corresponding predicate defined on
objects and P¯ 2 P¯ the one defined on PPs. For example, the property RED (being red)
in P would be represented by the predicate RED in P or by the predicate RE¯ D in P¯ . As
said, the redness of the rose r can be formally represented by RED(r) (“the rose r is of
type red”) or by 9p(INH(p; r) ^ R E¯D(p)) (“the rose r has a property particular of type
redness inhering in it”). Notice that, in principle, some of the predicates in P and P¯ could
be FOL-definable in terms of other predicates. We do not consider this interesting aspect
that requires a deeper analysis of the links between the considered properties, here we
focus only on taxonomical relations between properties.</p>
      <sec id="sec-3-1">
        <title>3.1. Specialization</title>
        <p>Specialization, e.g., the property being red specializes the property being colored (COL),
is one of the main taxonomical relation. Suppose one wants to represent the fact that the
property P 2 P specializes the property Q 2 P , i.e., intuitively, the fact that an object
being P is also Q. We analyze below different options to model this fact and, in Sect. 4.2,
how these options are intertwined with the question of the identity of PPs.</p>
        <p>In FOL specialization is usually represented by material implication, i.e., one would
consider the predicates P; Q 2 P corresponding to the properties P and Q and introduce
an implication axiom from P to Q. Let S be the set of couples of properties in P that
the user assumes to be linked by a specialization relation4 and S the set of couples of
predicates in P corresponding to the couples in S (similarly for S¯ ). The specializations
relations in S can be represented by introducing the axiom (cspec), stating that if A
specializes B, i.e., (A; B) 2 S , then an object that is A is also B.</p>
        <p>(cspec) V(A;B)2S 8a(A(a) ! B(a))</p>
        <p>Having PPs in the domain of quantification opens new options. One can start from
a basic requirement where the specialization is seen as a generic existential dependence
4Note that we will not address in this article the question of determining which properties should enter in
P, and in particular which predicates should be linked by a specialization relation (that is, which couple of
predicates should be included in S ); in particular, we will not address the question of determining whether we
can associate a predicate to each predicative linguistic expression, and whether a PP should be associated to
each predicate. In addition, we assume here that specialization is at least a partial order relation with no loops.
between PPs inhering in the same object, i.e., one can introduce the axiom (spec) (where
p and q range over PPs), stating that if there is a PP p of type A¯ inhering in an object a,
then there is a PP q (which might be different from p) of type B¯ inhering in a.
(spec) V(A¯;B¯)2S¯ 8pa( A¯(p) ^ INH(p; a) ! 9q( B¯(q) ^ INH(q; a)))
(spec) is very permissive on the existence of PPs. Suppose from now on that
( P¯; Q¯) 2 S¯ . (spec) is compatible with the facts that either (i) P¯-PPs are included in Q¯-PPs
or (ii) P¯ -PPs are disjoint from Q¯-PPs (it is also compatible with a proper subset of P¯-PPs
being included in Q¯-PPs, but we will not consider this option here). (spec) can then be
refined by adopting one of the two (incompatible) options, i.e., the specializations relations
in S can be represented by introducing the axiom (incl spec) or, alternatively, the axiom
(disj spec) where S¯ is the set of proper specializations, i.e., S¯ = S¯ n f( A¯; A¯) j A¯ 2 P¯ g.
(incl spec) V(A¯;B¯)2S¯ 8p( A¯(p) ! B¯(p))
(disj spec) (spec) ^ V(A¯;B¯)2S¯ :9p(A¯ (p) ^ B¯ (p))</p>
        <p>According to (incl spec), if a PP is associated with a property, then it is also
associated with all the properties it specializes, e.g., a P¯ -PP is also a Q¯-PP. This amounts to
require the identity between p and q in (spec). In the rose example, all RE¯ D-PPs are also
CO¯ L, but it is possible to have CO¯ L-PPs that are not RE¯ D.</p>
        <p>According to (disj spec), PPs are specific to a given property: if P (properly)
specializes Q, a P¯ -PP is not a Q¯ -PP. In the rose example, it is not possible to have PPs that
are instances of both RE¯ D and CO¯ L. However, (disj spec) (as well as (incl spec)) allows
for the existence of several RE¯ D-PPs and of several CO¯ L-PPs inhering in the rose.5</p>
        <p>An interesting extension of the proposed framework would be to assume that the
user distinguishes specialization from correlation. These two relations could then be
represented differently, for instance, one could consider (incl spec) for specialization and
(disj spec) for correlation.</p>
      </sec>
      <sec id="sec-3-2">
        <title>3.2. Covering</title>
        <p>A second important taxonomical relation is covering. While specialization concerns the
way more specific properties are related to more generic properties, covering is intended
to cope with the opposite mechanism. Intuitively, when a property Q is covered by n
properties Pi (with i 2 f1; : : : ; ng) then all the objects having the property Q also have (at
least) a Pi-property. For simplicity, consider the case with n = 2, i.e., Q is covered by
P1 and P2 both different from Q. For example, in the case of the rose, assume that being
colored is covered by being red and being yellow. Similarly to the case of specialization,
C represents the set of triples of properties linked by the covering relation, while C and
C¯ are the corresponding sets of triples of properties in, respectively, P and P¯ .</p>
        <p>Classically, one could represent the being covered of Q by P1 and P2 by considering
the predicates Q; P1; P2 2 P and by adding an implication from Q to the disjunction of P1
and P2, i.e., one would add the following axiom (ccov) (where a ranges over objects).</p>
        <p>5 An additional interesting possibility is to have a specific existential dependence SD between PPs: SD(p; q)
stands for ‘the PP p specifically depends on the PP q’, where SD(p; q) ^ SD(p; r) ! q = r. One could then
introduce V(A¯;B¯)2S¯ 8pa(A¯(p) ^ INH(p; a) ! 9q(q 6= p ^ SD(q; p) ^ B¯(q) ^ INH(q; a))). This would allow to specify
the links between the different PPs.</p>
        <p>(ccov) V(A;B1;B2)2C 8a(A(a) ! (B1(a) _ B2(a)))</p>
        <p>Note that this does not mean that all the material implications with form A(a) !
(B1(a) _ B2(a)) are cases of covering. As a matter of fact, covering has an intensional
aspect that is not captured by (ccov) (indeed, this is also true in the case of (cspec) for the
specialization relation). For instance, one could think that being colored is not covered
by being 1kg heavy and not being 1kg heavy.</p>
        <p>Considering PPs, similarly to specialization, covering can be modeled by
introducing a generic existential dependence, i.e., by introducing (cov) according to which the
existence in the object a of a PP associated with a given property implies the existence
of a PP inhering in a associated with one of its covering properties:
(cov) V(A;B1;B2)2C¯ 8pa(A¯ (p) ^ INH(p; a) ! 9q(( B¯1(q) _ B¯2(q)) ^ INH(q; a)))
Similarly to (spec), (cov) can be refined in the two following ways: (i) (incl cov)
guarantees that a PP associated with a property is also associated with one of its covering
properties; (ii) (disj cov) assures that the existence of a PP associated with a property
implies the existence of a different PP associated with one of its covering properties:
(incl cov) V(A;B1;B2)2C¯ 8p( A¯(p) ! (B¯ 1(p) _ B¯ 2(p)))
(disj cov) (cov) ^ V(A;B1;B2)2C¯ 8p(:9p( A¯(p) ^ (B¯ 1(p) _ B¯2(p))))</p>
        <sec id="sec-3-2-1">
          <title>In the example of the rose:</title>
          <p>– according to (incl cov), when we have C O¯L(pr) we also have R E¯D(pr) _ YE¯ L(pr),
i.e. pr represents also either the being red of r or its being yellow.
– (disj cov) allows for general PPs that satisfy CO¯ L but neither RE¯ D nor YE¯ L; that is,
PPs associated only with the general colored character of the rose. However, from
the existence of this general PP, we can deduce the existence of a different, more
specific PP associated with either the redness or the yellowness of the rose.</p>
        </sec>
      </sec>
      <sec id="sec-3-3">
        <title>3.3. Combining Specialization and Covering</title>
        <p>Suppose now to represent the situation where Q is covered by P1 and P2 and where P1
and P2 are both specializations of Q. For the predicates defined on objects, by combining
(cspec) with (ccov), we obtain 8a(Q(a) $ (P1(a) _ P2(a))).</p>
        <p>For the predicates defined on PPs we obtain two consistent options:
– f(incl spec), (incl cov)g reduces to V(A;B1;B2)2C¯ 8p( A¯(p) $ (B¯ 1(p) _ B¯ 2(p))),
– f(disj spec), (disj cov)g reduces to a mutual existential dependence between the
PPs that are instances of a property and the (different) PPs that are instances of
one of the covering properties.</p>
        <p>These positions have several important features. First, in all the positions considered,
independently of the level of specificity of the PPs, it is possible to have different PPs
(inherent in the same object) instantiating the same PP-predicate, i.e., there could be p,
q, and a such that INH(p; a) ^ INH(q; a) ^ A¯ (p) ^ A¯ (q) ^ p 6= q.</p>
        <p>Second, (incl spec) guarantees that the PPs that instantiate a given PP-predicate A¯
also instantiate all the PP-predicates specialized by A¯, i.e., all the predicates B¯ such that
( A¯; B¯ ) 2 S¯ . However, it allows for PPs that instantiate a given predicate without
instantiating any more specific PP-predicate. The addition of (incl cov) rules out this last
possibility for those PPs associated with a covered property.</p>
        <p>Third, (disj spec) does not allow a PP to be an instance of two different PP-predicates
one specializing the other. Actually, (disj spec) does not even guarantee that the number
of the instances of a given PP-predicate is greater than the number of the instances of
its specializations: it is possible to have different specific PPs for only one generic PP,
e.g., there could be different RE¯ D-PPs and only one CO¯ L-PP (inhering in the same
object). To avoid that, one could specialize (disj spec) by introducing a specific existential
dependence as done in footnote 5. Similar considerations hold for (disj cov).</p>
        <p>All the options discussed are compatible with a quite strong multiplicativism of
PPs—that is, many PPs can be associated with the same pair (ob ject; pro perty). The
next section will therefore discuss which principle of restriction on the identity of PPs
could be endorsed to limit this multiplicativism.</p>
      </sec>
    </sec>
    <sec id="sec-4">
      <title>4. Restrictions on the Identity of Property Particulars</title>
      <sec id="sec-4-1">
        <title>4.1. A Strong Principle of Identity</title>
        <p>As observed at the end of Sect. 3, nothing prevents the possibility to have different PPs
(inherent in the same object) all instantiating the same predicate in P¯ . However,
intuitively, one could think that any object can satisfy any property in at most one way, i.e.,
there is a maximum of one PP for each couple (object; property). To formalize this
intuition one could introduce the axiom (idpp).</p>
        <p>(idpp) (INH( p; a) ^ INH(q; a) ^ WA¯2P¯ ( A¯( p) ^ A¯(q))) ! p = q</p>
        <p>In general, (idpp) is consistent with all the options introduced in Sect. 3. When
combined with (incl spec), it prevents the possibility to have several PPs inherent in the
same object at different levels of specificity. In the rose example, if we suppose RE¯ D(pr),
it follows that C O¯L(pr) and, by (idpp), pr is the unique CO¯ L-PP inhering in r, i.e., in that
case it is impossible to have a PP associated with the colored character of r that would
not be associated with the redness of r.6</p>
        <p>In the case of the red rose r we are then left with two options:
(1) in f(incl spec), (idpp)g there is only one PP pr that satisfies RE¯ D(pr) ^ CO¯ L(pr),
(2) in f(disj spec), (idpp)g there are two PPs pr 6= qr such that RE¯ D(pr) ^ CO¯ L(qr).</p>
        <p>
          In (1) pr concerns both properties being colored and being red. Consequently,
(idpp) forces a one-to-one mapping between PPs and (object; property) couples only
in the presence of (disj spec). Another constraint brought by (1) concerns the relation
of specialization. Assume, for example, that having a mass is represented by MA¯SS
and that there exists a predicate M¯C such that MA¯SS and CO¯ L specialize M¯C, that is,
(MA¯SS; M¯C); (CO¯ L; M¯C) 2 S¯ . If CO¯ L and MA¯SS are disjoint (as they should intuitively be),
there could not be two PPs ca and ma inhering in the same object a such that CO¯ L(ca) and
6It is logically possible to have CO¯ L(pr) ^ :RE¯ D(pr), but this implies that the rose has no RE¯ D-PP, i.e.,
:9p(RE¯ D(p) ^ INH(p; r)), and this ontology would not formalize adequately the redness of the rose. Adding
(incl cov) would even worsen the situation because CO¯ L(pr) ^ :RE¯ D(pr) would imply YE¯ L(pr).
MA¯SS(ma): otherwise, we would deduce by (incl spec) that M¯C(ca) and M¯C(ma), and by
(idpp) we would have ca = ma. A suggestion could be that the relation of specialization,
as well as the relation of covering, should be reserved for pairs of PP-types that are of
kind determinate/determinable [
          <xref ref-type="bibr" rid="ref11">11</xref>
          ], an interesting point left for future work.
        </p>
      </sec>
      <sec id="sec-4-2">
        <title>4.2. A Leibnizian Principle of Identity</title>
        <p>An alternative view to (idpp) would be to allow the existence of multiple instances
(inhering in the same object) of a given PP-predicate only when such predicate is
specialized by other PP-predicates. In the case of the red rose, one would have a single RE¯ D-PP
pr, that would also be a CO¯ L-PP; and a second, different CO¯ L-PP qr, that would not be
an instance of any specialization of C O¯L.7 This kind of ontology would be compatible
with the axiom (idall) below, a sort of restricted Leibniz principle that assures that two
PPs (inhering in the same object) are identical only when they are indistinguishable by
means of PP-predicates.</p>
        <p>(idall) (INH(p; a) ^ INH(q; a) ^ VA¯2P¯ ( A¯(p) $ A¯(q))) ! p = q</p>
        <p>First note that (idall) is weaker than (idpp): (idall) (but not (idpp)) allows for two
different PPs pr and qr such that CO¯ L(pr), R E¯D(pr), CO¯ L(qr), :R E¯D(qr), and pr 6= qr.</p>
        <p>Second, in general (idpp) does not imply (idall). Consider PPs p and q and object
a such that INH(p; a), INH(p; a), p 6= q, and VA¯2P¯ (:A¯ (p) ^ : A¯(q)). In this case (idpp)
vacuously hold, but (idall) does not hold. However in the reasonable assumption that all
PPs are classified under at least one predicate in P¯ , (idpp) implies (idall). Consider PPs
p and q and object a such that INH(p; a), INH(q; a) and VA¯2P¯ ( A¯(p) $ A¯(q)). By our
assumption, all PPs are classified under at least one predicate in P¯ . Suppose A¯(p) holds.
From the equivalence just mentioned, we can deduce A¯ (q). And from A¯(p) and A¯ (q), we
deduce by (idpp) that p = q. Thus, we have proved (idall).</p>
        <p>Third, f(disj spec), (idall)g is equivalent to f(disj spec), (idpp)g when all the
predicates in P¯ are disjoint and each PP is classified under at least one predicate.</p>
        <p>To summarize, we can distinguish at least four theories: T1 = f(incl spec), (idpp)g,
T2 = f(disj spec), (idpp)g, T3 = f(incl spec), (idall)g, and T4 = f(disj spec), (idall)g to
each of which we can add an axiom to deal with the cases of covering, (incl cov) or
(disj cov). For our discussion about the adequacy of these theories for modeling the
epistemic vs. realist view, we will not consider T4, which is quite close from T2.</p>
      </sec>
    </sec>
    <sec id="sec-5">
      <title>5. Realist vs. Epistemic Interpretations of the Three Theories of Identity</title>
      <p>To further illustrate T1-T3, suppose that the rose r is not only red, but more precisely it
is scarlet (SCA) and that (RE¯ D; C O¯L); (SC¯ A; RE¯ D) 2 S¯ . To represent this situation, a theory
should accept at least one PP associated with its colored character, one PP associated
with its redness, and one PP associated with its scarletness. The next question is whether
1
some of those PPs are identical or not. According to T1, there can be only one PP sr
7A weaker version would be to accept a first CO¯L-PP qr that would be specifically existentially dependent
on pr, in the sense discussed in footnote 5; and a second CO¯L-PP q0r that would not be specifically existentially
dependent on any instance of any specialization of CO¯L.
characterizing at the same time the scarletness, the redness and the colored character of
r. According to T2, there must be three different PPs: s2r characterizing its scarletness
only (but neither its redness nor its colored character), r2r characterizing its redness only,
c2r characterizing its colored character only. Finally, T3 is compatible with the existence
of three PPs: s3r characterizing its scarletness, redness and colored character, c3r
characterizing its redness and colored character, r3r characterizing its colored character only (it
is also compatible with a more economical ontology including only s3r, but it would then
collapse to the same ontology as the one implied by T1).</p>
      <p>
        There are at least two broad perspectives to interpret PP-constants: an informational
or epistemic perspective where PP-constants are intended to refer to pieces of
information, observations or cognitive categorizations; and a realist perspective, where
PPconstants are intended to refer to entities existing in the world (most of which are not
informational, although some of them may be so). We will not discuss in detail the
distinction between the two approaches (see, e.g., [
        <xref ref-type="bibr" rid="ref12 ref13">12,13</xref>
        ] for a related debate), but instead
comment on which theory seems to fit with which perspective, acknowledging that definitive
conclusions require more extensive investigations.
      </p>
      <p>T1 seems to make more sense when interpreted in a realist perspective than in an
epistemic perspective: s1r would represent the unique color of the rose, in its full
specificity. T2 may fit more naturally an epistemic perspective: s2r, r2r and c2r would represent
pieces of information on the color of an object acquired by measurement instruments
with different resolutions. The inference from the existence of s2r to the existence of r2r
could amount to the deduction of the information that the rose if red from the information
that the rose is scarlet. It might also be possible to interpret T2 in a realist perspective, if
one sees a statement like R E¯D(r2r) as expressing that r2r is the most specific entity
warranting the inference that the rose is red: in this ontology, the two other PPs s2r and c2r would
be respectively the most specific entity warranting the inference that the rose is scarlet,
and the most specific entity warranting the inference that the rose is colored. T3 seems to
be interpretable in both perspectives. In a realist perspective, c3r could be viewed as the
general structure responsible for the colored character of r, whereas r3r (resp. s3r) could
be viewed as the more specific structure responsible for its red (resp. scarlet) character,
which is also responsible for its colored (resp. red and colored) character. In epistemic
terms, c3r could represent the information collected by a device that could only detect
the colored character of an object, r3r to the information collected by a device resolving
being red and categorizing the redness as a color, and s3r to the information collected by
a device that would resolve being scarlet, and categorize it as a redness (and as a color).</p>
      <p>As we said, covering axioms can be added to those theories. Suppose that we add
(incl cov) to T3 and that (CO¯ L; RE¯ D; YE¯ L); (RE¯ D; SC¯ A; CR¯ I) 2 C¯ (including the color
crimson CRI). It is easy to see that, in the rose example, there is only one possible
configuration of PPs, namely a single PP s1r characterizing at the same time the scarletness, the
redness and the colored character of r, i.e., SC¯ A(s1r), R E¯D(s1r) and CO¯ L(s1r). That is, in
presence of (incl cov) and covering axioms between the relevant properties, the ontology
compatible with T3 will collapse to the ontology compatible with T1.</p>
    </sec>
    <sec id="sec-6">
      <title>6. The Reification of PP-types</title>
      <p>We will now sketch an alternative representation method that reifies PP-predicates and
is able to represent direct vs. indirect classification under a property. In an epistemic
view, this method allows to clearly separate the information acquired from measurement
devices from the one deduced from such information by using some general knowledge.</p>
      <p>Up to now, the PPs corresponding to a property P has been collected by means of
the PP-predicate P¯ . We now reify PP-types into the domain of quantification. For this, we
introduce a new kind of entities—PT(t) stands for “t is a PP-type”—and we assume that
there is a one-to-one correspondence between the properties in P and the PT-constants
in the set PPT. We note p 2 PPT the PP-type corresponding to P 2 P.8</p>
      <p>The general idea is that PPs are classified by PP-types. In particular we consider the
primitive relation of direct classification between PPs and PP-types: dCF(p; t) stands for
“the PP p is directly classified under the PP-type t” (a4). We assume that PPs may have
a unique direct PP-type, i.e., they can be directly classified under a single PP-type (a5).
a4 dCF(p; t) ! PP(p) ^ PT(t)
a5 dCF(p; t) ^ dCF(p; u) ! t = u</p>
      <p>The specialization relation between properties is represented by the partial order
v defined between PP-types: t v u stands for “the PP-type t is a specialization of the
PP-type u”. The specialization relations in S are modeled by introducing (ptspec) where
SPT is the set of couples of PT-constants corresponding to the couples in S .
(ptspec) V(a;b)2SPT a v b</p>
      <p>Crucially, in this framework it is possible to make the difference between the
abovementioned direct classification and the indirect classification (iCF) defined in (d1).</p>
      <p>d1 iCF(p; t) , 9u(dCF(p; u) ^ u v t)
The general case where ‘a is P’ is then modeled using indirect, rather that direct,
classification, i.e., by 9q(INH(q; a) ^ iCF(q; p)), where p represents the property P.9 In the
example of the rose, dCF(pr; red) together with red v col imply iCF(pr; col). The
indirect classification iCF allows then to explicitly represent classifications grounded on
knowledge about the specialization relation. First note that iCF does not require the
existence of any additional PP. Second, this framework is compatible with the existence
of PPs pr and qr (both inhering in the rose) such that iCF(pr; col) and dCF(qr; col),
i.e., the existence of a PP directly classified under a given PP-type does not exclude the
possibility to have a different PP directly classified under a more general PP-type.</p>
      <p>This theory is similar to T3 where the previous situation may be represented by
RE¯ D(pr) ^ C O¯L(pr) together with :R E¯D(qr) ^ CO¯ L(qr). Note however that in T3 we don’t
really have a notion of indirect classification, we just have the PPs pr and qr that are both
standardly classified under C O¯L while pr, but not qr, is also standardly classified under
RE¯ D. Here all the atomic assertions have the same ‘status’ and one can establish the level
of resolution of a given assertion only by looking at the other assertions present in the
theory. On the other hand, by reifying PP-types, it is possible to direclty manage
different kinds of classification of PPs (different classification modalities) by means of several
relations defined between PPs and PT-instances. Furthermore, the fact that the
specialization relation is also represented by a relation (v) leaves space for a more intensional</p>
      <sec id="sec-6-1">
        <title>8Variables/constants ranging over P-types are noted t; u; : : : ; t; u; : : :</title>
        <p>9Given the reflexivity of v, dCF(p;t) ! iCF(p;t), i.e., direct classification is a limit case of indirect
classification.
characterization of this relation. Future work should investigate the possible benefits of
the reification strategy.</p>
      </sec>
    </sec>
    <sec id="sec-7">
      <title>7. Conclusion</title>
      <p>We have thus identified three theories of identity among PP, and characterized with which
perspective (epistemic or realist) they appear to be compatible. We have presented a
reification of property-types that enables to formalize how PPs can be directly or indirectly
classified under property-types. Future work should investigate more closely various
theories about 1) what counts as a property 2) which of those properties are linked by a
specialization relation and 3) how the distinction determinate/determinable can shed light on
the application of our formalization to various theories of properties and specialization.
It should also investigate further the benefits that the reification of property types could
bring. The question of the diachronic identity of PPs will also need to be addressed:
PPs are generally considered as continuants, that persist in time by being fully present
at each instant; but what are the criteria for two PPs at different times to be the same
entity? This investigation on the identity of PPs should also be refined into more
specific investigations about the identity of complex properties such as roles, functions and
dispositions.</p>
    </sec>
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