<!DOCTYPE article PUBLIC "-//NLM//DTD JATS (Z39.96) Journal Archiving and Interchange DTD v1.0 20120330//EN" "JATS-archivearticle1.dtd">
<article xmlns:xlink="http://www.w3.org/1999/xlink">
  <front>
    <journal-meta>
      <journal-title-group>
        <journal-title>F. C. Pereira, A. Cardoso, The boat-house visual blending experience, in: Proceedings of the
Symposium for Creativity in Arts and Science of AISB</journal-title>
      </journal-title-group>
    </journal-meta>
    <article-meta>
      <article-id pub-id-type="doi">10.7551/mitpress/9629.001.0001</article-id>
      <title-group>
        <article-title>A Cloud Full of Paths: Conceptual Blending as Betweenness Relation</article-title>
      </title-group>
      <contrib-group>
        <contrib contrib-type="author">
          <string-name>Mena Leemhuis</string-name>
          <email>Mena.Leemhuis@unibz.it</email>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Oliver Kutz</string-name>
          <email>Oliver.Kutz@unibz.it</email>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <aff id="aff0">
          <label>0</label>
          <institution>Free University of Bozen-Bolzano</institution>
          ,
          <addr-line>Piazza Università 1, Bolzano</addr-line>
          ,
          <country country="IT">Italy</country>
        </aff>
      </contrib-group>
      <pub-date>
        <year>2002</year>
      </pub-date>
      <volume>2002</volume>
      <issue>7</issue>
      <fpage>207</fpage>
      <lpage>220</lpage>
      <abstract>
        <p>Image schemas are vital for embodied cognition. In addition to image schemas considering one object or the interplay between two objects, there are also some having a ternary nature and allowing for the definition of some form of betweenness, such as for instance the introduction of a goal in between a start- and endpoint of a path. Betweenness is a central notion both in cognitive and formal aspects of modeling concepts. For example, in conceptual spaces, an object in between two other objects belonging to some concept again belongs to that same concept, according to the convexity assumption. This kind of betweenness understood as a path-searching procedure allows for increasing the comprehensibility of the resulting in-between objects because of a better understanding of the creation and origin of those objects. This view can also be applied to the task of finding new, creative objects based on given ones, thus finding paths that are not the straightforward solution, that is, not within a given convex conceptual space. This ofers a direct connection to the framework of conceptual blending which allows for a structured creation of a blend of two input objects. We show that blending can be interpreted as a betweenness relation and that this path-based view is helpful to allow for a diferent viewpoint on conceptual blending. We argue that conceptual blending defined in this way as betweenness fulfills basic betweenness axioms and is thus a viable betweenness relation. As a proof of concept, these considerations are applied to visual blending.</p>
      </abstract>
      <kwd-group>
        <kwd>eol&gt;conceptual blending</kwd>
        <kwd>image schemas</kwd>
        <kwd>betweenness</kwd>
        <kwd>generative models</kwd>
      </kwd-group>
    </article-meta>
  </front>
  <body>
    <sec id="sec-1">
      <title>1. Introduction</title>
      <p>
        Image schemas [
        <xref ref-type="bibr" rid="ref1 ref2">1, 2</xref>
        ] can be seen as semantic building blocks of embodied cognition and early
generalizations of experiences and therefore ofer a direct link between embodied experiences and cognitive
representations. An example is the image schema Support, denoting that an object is supported by
another object, e.g., a cup on a table. Although many image schemas consider one object or the interplay
between two objects, there are also image schemas such as Link and Source_Path_Goal that are
ternary in nature, describing two (abstract or concrete) linked objects resp. a path from a source to a goal.
Next to the two connected objects, there is a third object, namely the link resp. the path in between those.
Considering the link resp. path as part of the image schema allows for achieving a deeper understanding
of the scenery: it can be determined whether an intermediate goal is on the path, thus in between
source and goal of the path, leading to the image schema Source_Path_via_Goal. Understanding Link
means that children learn that when pulling on some object connected through a physical link with
another object (a special case of Link), then, in addition to these two objects, also all objects in between
them will move. Thus, betweenness, though not typically characterized as an image schema, is of vital
importance for embodied cognition. However, betweenness is not restricted to this spatio-temporal view.
It can also be used to decide on an abstract level whether some object is in between another two objects,
e.g., in form of interpolation between rules: if it is known that a flat is cheap and a villa is expensive
and it is known that a townhouse is in between a flat and a villa, then it can be concluded based on
an assumed betweenness that a townhouse has a moderate price [
        <xref ref-type="bibr" rid="ref3">3</xref>
        ]. This principle of convexity of
cognition has, e.g., been proposed by Gärdenfors in his theory of conceptual spaces [
        <xref ref-type="bibr" rid="ref4">4</xref>
        ]. He states that
luxury flat
g
n
i
h
s
i
n
r
u
f
furnishing&amp;size
mid-range
townhouse
cheap flat
size
expensive villa
run-down villa
concepts are cognitively represented as convex (thus, betweenness-closed) sets and that especially
learnability is increased by considering convex representations [5]. Schockaert and Prade [
        <xref ref-type="bibr" rid="ref3">3</xref>
        ] state
that betweenness also allows for finding new in-between representations in conceptual spaces, e.g., for
completing an incomplete rule base. Also this abstract notion of betweenness can be considered from
an image schematic viewpoint, namely as a special type of the image schema Source_Path_via_Goal:
If for two given objects an in-between representation is searched for, this process can be considered as
a path-finding problem where a goal needs to be determined that is in-between the two objects, thus on
an (abstract) path connecting them. In the example mentioned above, visualized in Figure 1, this would
be the straight black line denoting a betweenness based on size and furnishing.
      </p>
      <p>
        This straight connection denoting a straightforward and expected betweenness is not the only
possibility. Beside the moderately priced houses (which are justified by the knowledge base) one
could think of more creative and less justified results, such as a cheap villa or an expensive apartment.
Therefore, since the novel combination of familiar ideas can be seen as a fundamental aspect of human
creativity [6], choosing diferent betweenness relations enables a creative combination of given objects.
Thus, the path of thought may take some detours to obtain creative results. This process is creative, as
it allows for a wider variety of in-between objects and is not restricted to plausible results grounded in
given background information as, e.g., the rule-base completion approach [
        <xref ref-type="bibr" rid="ref3">3</xref>
        ]. Analyzing the chosen
path helps in understanding the creatively invented new object, as it allows for considering the iterative
changes starting from start or end. However, the resulting path should be creative but not arbitrary,
as, e.g., a creative combination of a house and a boat being a pink apple would not be considered as
creative but as implausible and out of context. One type of betweenness suitable for this task is the
intersection betweenness [7]: Roughly, it is defined such that some object is in between two other
objects if the in-between object has all attributes the other two objects have in common. Thus, the
creativity would be grounded on common attributes and thus would be more plausible. The problem
is, however, that the intersection betweenness needs an attribute representation of both inputs and
considers the intersection of these representations. Such a representation is not always available and the
intersection is a too strong restriction, as it, e.g., does not consider generalizations of attributes which
then may coincide. Following the basic principles of intersection betweenness while dismissing the
representation of concepts as sets of attributes can be directly considered as a version of the framework
of conceptual blending, as discussed by Fauconnier and Turner [8]. The basic idea is that two input
concepts (e.g., “house” and “boat”) are combined to form a new concept (typically not unique), e.g.,
“boathouse” or “houseboat”. The first step is to find an abstraction of the commonalities of the two
input concepts, the so-called generic space. Then, a blend is created, based on the information of the
generic space and enriched with some features of the input spaces. Conceptual blending is a highly
researched area, both in theory and in practice (see, e.g., [9]). When comparing the process of conceptual
blending with the betweenness relation, especially with the intersection betweenness discussed above,
the similarity becomes evident: the generic space serves a function analogous to the intersection of
attributes in the intersection betweenness (however, is not unique and allows for generalizations) and
a blend can be considered as an object in between. This leads to the main statement of this paper:
conceptual blending can be considered as a betweenness relation and therefore, in an image schematic
view, the blending process can be seen as a search for a suitable path between two inputs, passing
by the blend. As betweenness is an important notion, formally introduced by Huntington and Kline
[10] and used in many diferent use cases, an interpretation of conceptual blending as betweenness
allows to exploit this literature. It especially allows for a combination of the classical symbolic view
of conceptual blending with a subsymbolic view of the betweenness relations and thus enables to
incorporate the rich semantic structure of the subsymbolic space by meanwhile keeping the advantages
of conceptual blending regarding conceptualization and reliance on a generic space. Additionally,
the path-based view allows for understanding the creation of the blend by “walking the path”, thus
iteratively comprehending the changes necessary between start and end to reach the goal. As a proof
of concept, an interpretation of visual blending as betweenness relation is given which shows that the
process can profit from considering betweenness relations and their properties.
      </p>
      <p>The rest of the paper is structured as follows: After a short introduction to image schemas, the
importance of betweenness in an image schematic and general cognitive viewpoint is pointed out. After
that, a short overview on conceptual blending is given, its connection to betweenness is discussed and
necessary properties of the resulting betweenness relation are given. The last section considers an
application to visual blending. The paper ends with a conclusion and an outlook.</p>
    </sec>
    <sec id="sec-2">
      <title>2. Image Schemas and Betweenness</title>
      <p>
        Image schemas ofer a direct link between embodied experiences and representations in the mind and
are therefore a basic semantic building block of embodied cognition. They have been independently
introduced by Lakof [
        <xref ref-type="bibr" rid="ref1">1</xref>
        ] and Johnson [
        <xref ref-type="bibr" rid="ref2">2</xref>
        ]. Image schemas are said to be learned in early infancy and
are thus preverbal [11]. Therefore, image schemas can be seen as early generalizations of experiences.
Examples for image schemas are Support, expressing the fact that an object is supported by another one,
and Containment, thus the notion that an object can be placed inside another object without falling
out. Next to the spatio-temporal use of image schemas, they also found their way into language in form
of metaphors: “to be in love” is an example for an abstract use of the image schema Containment.
      </p>
      <p>Image schemas such as Support and Contact are included in the two-object family as introduced
and discussed in [12]. Thus, they are based on the interaction between two objects . Link is a member
of this family and represents an “enforced connection between objects or regions, where transitivity
ensures that the linked object reacts to the stimuli of the other object” [12]. It could be a concrete link
like, e.g., a rope, or an abstract link like an emotional binding between persons or any form of causal
relationship. A member of the Path-family is Source_Path_Goal, relating to movement from a source
to a goal, including spatial primitives such as a path between them [12].</p>
      <p>Although, these image schemas are on first sight based on two objects (the two linked objects, resp.
source and goal), they actually incorporate a more complex relationship. Both include a third important
element, namely the connection of the two objects, either the (possibly abstract) link or the path. Thus,
Link and Source_Path_Goal are examples of image schemas that are ternary in nature. Therefore,
though image schemas comprise basic notions easily perceptable, some elements of ternarity are needed.
This becomes even more obvious for the image schema Source_Path_via_Goal where there is a goal
in between the start and end of the path (see Figure 2 for an illustration).</p>
      <p>Those three image schemas have an implicit notion of betweenness incorporated. Betweenness is
not an image schema by itself and already a quite complex notion, however, Source_Path_Goal and
Link require at least basic knowledge of special cases of betweenness. A child may consider the points
in between source and goal on a path and may recognize beforehand that they will pass these points.
They may even be able to consider diferent paths, thus diferent betweenness relations, and choose the
best one. They are also able to recognize (at least for physical links) that an interaction with one linked
object not only influences the other linked object but possibly also the objects in between. Therefore, it
can be concluded that betweenness is at least implicitly incorporated in the catalog of image schemas.
Source_Path_Goal can also be interpreted metaphorically, such as in “life is a journey”. There, as
in the concrete case, the main point of this expression is not the source and the goal (thus, birth and
death) but the path in between, all those experiences, one following another, on this journey. Whether
betweenness should be considered an image schema by itself, or whether it is a too complex or abstract
notion in its full generality, is an interesting question for future research.</p>
      <sec id="sec-2-1">
        <title>2.1. A Formal Notion of Betweenness</title>
        <p>A betweenness relation could be an arbitrary ternary relation. An object  is said to be in between
 and  (written (, , )). It has been formally introduced by Huntington and Kline [10] and is
based on an axiomatization of geometries by Hilbert [13]. Betweenness can be used to enrich the
underlying structure of a space with an order, e.g., to determine an order of sets [7] or as a basis for
ordered geometry. Another benefit of betweenness is that it allows for defining convex sets (in the sense
of betweenness-closure) and thus allows, e.g., for convex optimization. One well known betweenness
relation is the metric betweenness, e.g., in R</p>
        <p>(, , ) if (, ) + (, ) = (, ) for , ,  ∈ R with  ̸=  ̸= ,
based on a distance (· , · ), e.g., the Euclidean distance. With this betweenness, it is, in fact, possible to
develop, together with the notion of equidistance, the whole elementary geometry axiomatically and,
thus, it can be considered as a basic notion of elementary geometry [14]. Next to the metric betweenness,
betweenness can also be used, e.g., for checking properties of lattices [15] or for knowledge graph
embeddings with incorporation of expressive background logics [16] and in several other areas.</p>
        <p>Though betweenness relations can be arbitrary ternary relations, to strengthen their expressivity,
basic betweenness axioms have been considered to which an expressive betweenness relation should
adhere to. They have been introduced by Huntington and Kline [10]. In the following, some basic
betweenness axioms are presented.</p>
        <p>Definition 1. The following are basic betweenness axioms, based on a set  and , ,  ∈ 
(B0) If (, , ), then , ,  are pairwise distinct.
(B1) If (, , ), then (, , ).</p>
        <p>(distinctness)
(symmetry in the end points)
(B2) If (, , ) and , ,  are pairwise distinct, then not (, , ).
(non-exchangeability)</p>
        <p>There are many further axioms considered, useful for determining the exact properties of a specific
betweenness relation. One additional axiom concerns the density of the space, thus whether there is,
for any two distinct elements of the space, an element in between.
(C1) For any two distinct points  and  in , there is some point  such that (, , ).
(density)
Another axiom, particularly interesting, as it is fulfilled by the Euclidean betweenness, is the following,
stating that there is only one “path” in between two elements  and , thus that two objects  and ′
both in between  and  must be in a betweenness relation by themselves.
(C2) If for distinct  and ′, (, , ) and (, ′, ), then either (, ′, ) or (, , ′).
Though this is fulfilled by the Euclidean betweenness, it is a strong axiom not valid for every use case.</p>
      </sec>
      <sec id="sec-2-2">
        <title>2.2. Betweenness in Cognition</title>
        <p>Betweenness is implicitly incorporated into image schemas such as Source_Path_Goal and Link in a
spatio-temporal manner. Next to this spatio-temporal view, image schemas allow for a metaphorical
view directly resembling the spatio-temporal view in a metaphorical setting. However, these image
schemas can be viewed in an even more abstract way: Source_Path_via_Goal can also be considered
as a path between two objects trespassing several goals in form of other objects. When considering the
example in Figure 1, to figure out the price of a townhouse, it is possible to imagine a path between the
cheap flat and the expensive villa, changing furnishing and size successively, passing, e.g., a less cheap
apartment, a near too expensive small villa and also the mid-range townhouse which is the answer to
the question. This image-schematic view on betweenness allows for an understandable and explainable
result since the way the in-between object has been approached is comprehensible.</p>
        <p>
          As this imagined path does not need to have a direction, also the image schema Link is suitable in
this regard: a physical link between two objects can be defined based on the objects in between (e.g.,
the position and other features of the parts of the link, e.g., of a chain). In the same way, two objects
can be considered as being abstractly linked when there are objects in between. These in-between
objects define whether the link is a straightforward or creative one. The view of applying betweenness
to objects to obtain in between objects is justified by the consideration of conceptual spaces. They have
been introduced by Gärdenfors [
          <xref ref-type="bibr" rid="ref4">4</xref>
          ] and are based on the idea that cognition is geometrical and that
concepts are cognitively represented as convex sets (resp. combinations of convex sets). As convexity
can be defined as betweenness-closure, this directly leads to the consideration of objects as in between
other objects. This is motivated by cognitive economy and by the fact that inferring knowledge may
work as follows: If one knows that two objects have a specific property, then it is natural to assume that
an object in between the other two objects also has this property; this has been done for an incomplete
rule-base by Schockaert and Prade [
          <xref ref-type="bibr" rid="ref3">3</xref>
          ]. One betweenness relation particularly useful for cognitive
considerations is the intersection betweenness, a betweenness defined over sets of elements. Next to
considering sets in general, this definition of betweenness supports also the declaring of a betweenness
relation based on the attributes of objects. This is based on the idea that objects can be compared based
on sets of their features [7]. An object  is said to lie in between  and  if it shares the features common
to  and  (but may have ones that neither  nor  have) [17]. An example can be seen in Figure 3. Face
 is in between faces  and , as it shares the properties both have in common (the shape of the face
and the mouth) and additionally has some distinctive properties, namely the hair of  and the eyes of .
This intersection betweenness is perfectly in line with the interpretation of betweenness as a path, as it
is possible to iteratively change the first input to gain the in-between which then can iteratively be
changed to obtain the second input. Intersection betweenness on the concept level has been discussed
by Ibáñez-García et al. [18]. They argue in a description logic setting and state that a concept is in
between two other concepts, if it is in between based on intersection betweenness on the feature level.
        </p>
        <p>Even when considering intersection betweenness, there is not only the one possible path that is
justified by the background knowledge. Next to this, there are other paths, though not justified by
the data, however, acting as starting points to be creative: what would a cheap villa or an expensive
lfat look like? As creativity based on a new combination of two known concepts is a common way of
creativity [6, 19], it would be interesting not only to consider the justified object in between but also
other, more creative and less justified paths. However, these paths are not allowed to be arbitrary, in
fact, the creativity needs to be controlled to lead to reasonable results. An area where this is considered
is the area of conceptual blending. Therefore, in the following, it is discussed that conceptual blending
can be interpreted as such a path-finding betweenness problem and can profit from such a view.</p>
      </sec>
    </sec>
    <sec id="sec-3">
      <title>3. Conceptual Blending and Betweenness</title>
      <p>In the following, it is argued that conceptual blending can be considered as a special type of betweenness
relation. We begin with a quick reminder about conceptual blending.</p>
      <sec id="sec-3-1">
        <title>3.1. Conceptual Blending</title>
        <p>Conceptual blending was introduced by Fauconnier and Turner [20] and is a technique to achieve new
concepts by creatively combining existing ones. The basic idea is to consider two input spaces, containing
a representation of the input objects, e.g., “house” and “boat” such as that they have inhabitants, being
on top of water resp. land etc. With these inputs, a generic space is defined, containing some general facts
or abstractions that are common to both inputs. This space can be obtained through a generalization of
both input spaces and is thus a more powerful device than an intersection of attribute representations
as in intersection betweenness. The generic space is not unique, as diferent generalization strategies
could lead to diferent results. With the help of the generic space, the blend can then be created by
incorporating facts from both input spaces without contradictions. The last step is to “run the blend”,
thus to enlarge the blend with information not given in the input spaces. For the house-boat example, the
blend could be a houseboat and the running would incorporate questions such as how big a houseboat
would be or whether it could be used ofshore. The blend is again not unique, however, there are better
and worse blends. To determine the quality of a blend, so called optimality principles may be used [20].
An example is the unpacking principle which states that both input spaces need to be reconstructable out
of the blend, thus, that a suficient amount of information of both input spaces should be incorporated.
Therefore, a blend is of low quality if it is based solely on one input space and incorporates only a slight
adjustment towards the other one. For a comprehensive discussion of optimality principles, see [20].</p>
        <p>The formalization of conceptual blending is a challenging task, particularly the construction of the
generic space. An example is an approach proposed by Eppe et al. [9] based on answer set programming.
Although it was shown to work out for several examples, it is dificult to use in a general setting, as
it sufers from complexity issues. As this is a general problem of symbolic approaches for conceptual
blending, its interpretation with the help of betweenness could help to incorporate subsymbolic aspects
into the process to better handle the complexity of the problem.</p>
      </sec>
      <sec id="sec-3-2">
        <title>3.2. Conceptual Blending as Betweenness Relation</title>
        <p>As discussed above, betweenness can be used to be creative and to construct new objects based on given
ones. As betweenness relations have a wide variety of properties, such betweenness-based creativity
could also lead to many diferent more or less reasonable results. Therefore, it is necessary to restrict
the possible outcomes. This is the reason for considering conceptual blending: it creates out of two
input spaces not only a blend but also a generic space restricting the blend, prevents contradictory
results and allows for judging the quality of the blend with the help of optimality principles. However,
the advantages of the betweenness-based and especially the path-based view should be kept, therefore,
conceptual blending is interpreted as a special type of betweenness relation, related to intersection
betweenness: the blend can be considered as being in between the input spaces, as similar to the
intersection betweenness, there is an underlying space (the generic space) the blend must rely on
and additionally, the blend consists of properties of the two inputs. Thus, conceptual blending can
be considered as a generalization of intersection betweenness. However, there are vital diferences:
intersection betweenness is made for determining whether given objects have a betweenness relation.
Using it for creativity has several issues: First, it is based on attribute representations and thus does not
allow for the definition of an expressive generic space. Second, it is, even if the intersection of both
blend
generic space
input 1
input 2 input 1: house</p>
        <p>space of possible blends
instances of house instances of bottle
good
blends</p>
        <p>input 2: bottle
generic space: containment
inputs is considered to be reasonable, not given how to define a reasonable new object in between which
is expressive, creative and non-contradictory. Conceptual blending allows for all this and gives with
the optimality principles also hints on how to judge the quality of the blends. Therefore, conceptual
blending under this betweenness-based view can be interpreted as a path search from one input space
to the other whereas this path is not allowed to be arbitrary, as it is restricted by the underlying
generic space to which each object on the path needs to adhere to and additionally does not allow
for contradictory results. The basic idea of considering betweenness instead of conceptual blending
directly is to enable creating a blend in a more neuro-symbolic way. Whereas many conceptual blending
approaches are based on symbol manipulation, betweenness allows for many diferent viewpoints, e.g.,
based on numeric or other abstract representations of the objects, thus allows for using the advantages of
subsymbolic reasoning. Of course, betweenness alone does not lead to such viewpoints, it is additionally
necessary to have data in an adequate representation to be used as basis for a betweenness relation.
It would also be possible to interpret existing frameworks in a betweenness based setting. There are
representations, e.g., in latent spaces that could be good starting points for a search for a suitable
betweenness relation combining subsymbolic and symbolic information. This is discussed in Section 4.</p>
        <p>Next to this view, it is also possible to consider conceptual blending as combination of diferent
betweenness relations. This becomes evident when looking at the diagram of the framework of
conceptual blending (see Figure 4 on the left). There, a graph-based betweenness can be applied, stating
that a node is in between two other nodes if it lies on the shortest path between them on a graph. This
view leads to four diferent betweenness relations (1, , 2), (1, , 2), (, 1, )
and (, 2, ) (and their symmetric counterparts) where  denotes the generic space and
 the blend. In the following, the first two betweenness relations are looked at, as they match the
view of having the input spaces given and determining generic space and blend. For future work, a
consideration of the other two betweenness relations could also be interesting, e.g., for inverse blending
by determining possible input spaces for a given blend. These definitions are not only justifiable by this
abstract graph-based argument but also based on the basic principles of conceptual blending.</p>
        <p>Considering solely the betweenness relation (1, , 2) pictures classical strategies of visual
blending or image morphing where the basic idea is to combine two images on a visual level. Although,
it is also based on a smooth transition between the two input images, it has not the same expressivity as
conceptual blending, as the possible paths are not restricted based on a generic space and the focus does
not lie on conceptual knowledge. An example of this betweenness is discussed in detail in Section 4.</p>
        <p>The second betweenness, thus “the generic space is in between the two input spaces” is more abstract
and not as easily justifiable: The basic idea is again to find a plausible path from one input to the other,
in contrast to the betweenness of the blend with a diferent focus: instead of exchanging attributes of
one input space with attributes of the other, here the attributes of both input spaces are generalized
until they reach a point where both generalizations meet. This can be considered as a search for a Link.
One way of stating that two objects are linked is to find their commonalities, thus a generalization in
between them. This could also be interpreted as a basic case of intersection betweenness where only
the intersection of properties (in this case the generalization of input spaces) is considered without
adding further attributes from one or both of the inputs. In special cases this could be the outcome of a
conceptual blending process, e.g., when a compromise of two contrastive opinions is searched for. Then,
the generic space is the only possible blend, as all extensions would contradict the compromise. To use
these two betweenness relations for conceptual blending, it is necessary to find a combination of them.
Betweenness Axioms For underlining the adequacy of considering conceptual blending as
betweenness relation it is shown that betweenness based on the framework of conceptual blending fulfills
the basic betweenness axioms. An interesting application would be to interpret existing conceptual
blending methods as betweenness relations and to discuss their betweenness axioms in contrast to the
betweenness axioms of the basic framework of conceptual blending. This is, however, left for future
work. As there are many diferent betweenness axioms for diferent use cases, in the following, the
basic axioms (B0)–(B2) and (C1) are discussed for all three cases of betweenness mentioned above (if
not otherwise indicated, the explanation is applicable to all three). Additionally, to give a hint on the
fact that some classical betweenness relations, such as the Euclidean betweenness, could be unsuitable
for representing blending (even if a suitable geometric representation of the input spaces is found), the
axiom (C2) is considered which depicts a basic property of Euclidean betweenness which is, however,
in general too restrictive for conceptual blending. It turns out that all three basic axioms and the axiom
of density (C1) are fulfilled in a conceptual blending setting. This underlines the validity of interpreting
blending as a special type of betweenness relation.</p>
        <p>First, the axiom (B0), thus the distinctness of the elements of a betweenness relation is considered.
Clearly, the blend needs to be diferent from the two inputs, as otherwise no creativity is needed.
However, it is not as obvious whether a blend can be created based on only one input space: an example
is the blend of a dog leading to a dog with two heads. Even though the creation of the generic space is not
unique and there are several options of generalizations even for identical input spaces, the most natural
and thus also best generic space based on optimality principles would be a generic space identical to the
input. In this case, no creativity is possible. Therefore, it can be argued that a dog with two heads could
not be considered to be a blend of two dogs (at least not in the framework of conceptual blending).</p>
        <p>In the conceptual blending framework the order of inputs is not specified, therefore symmetry (B1) is
trivially valid. In a path-based perspective, this means that it does not matter whether the path starts at
the one input or the other. This underlines the image schematic viewpoint that instead of a path also an
(undirected) Link can be considered. It could be the case that the influence of one input is stronger than
the influence of the other, this is, however, not because of the position of the input as first or second
one but based on the properties of the input spaces.</p>
        <p>The non-exchangeability principle (B2) can be seen to follow assuming the unpacking principle
together with certain (contingent) features of blends, as follows: Assume, by contradiction, that both
relations of (B2) are valid, thus (1, , 2) and (, 1, 2). Due to the unpacking principle,
the blend needs to be influenced by both inputs, thus it has properties one of the inputs has and the
other does not. Thus, given (1, , 2), especially  and 2 are sharing some properties that 1
does not share, say property  is enjoyed by 2 but not by 1 (this also follows from the common
assumption in blending that there is some conceptual clash between 1 and 2). Now when considering
(, 1, 2) and the generic space created by  and 2, a natural condition of maximality of the base
implies that these shared properties are incorporated into this base space. Thus,  belongs to the base.
However, if that is the case, then since 1 inherits properties from the generic space (assuming complete
inheritance from base), it follows that 1 needs to have the property  , too. This is a contradiction
derived solely from the unpacking principle and certain maximality principles concerning the role of the
base, outlining the conditions for validity of the non-exchangeability principle. Studying in full detail
such dependencies between rules in blending construction and algebraic conditions on betweenness
relations will be the subject of future work.</p>
        <p>The above consideration shows that conceptual blending interpreted as betweenness relation fulfills
basic betweenness axioms which again underlines that such an interpretation is suitable, as it opens up
a wide choice of betweenness relations which could be useful for considering blendings.</p>
        <p>Besides the classical betweenness axioms, it is possible to consider other, more specific ones. The
axiom of density (C1) needs to be viewed from two perspectives: on the one hand, the two input spaces
could be highly similar. Then, the blending process does not result in an overly creative blend, however,
even for similar (but not equal) input spaces, a blend is possible. On the other hand, two input spaces
could be highly dissimilar. Then, the generic space is a coarse generalization depicting highly general
cases. This, however, is no restriction of the blending process, in fact, a coarse generic space allows for
creative blends. Therefore, all two objects allow for a blend and thus the density axiom is valid. The
quality of the blend, of course, depends on the chosen input spaces.</p>
        <p>Axiom (C2) depicts that there is only one path in between two inputs. This is not generally valid.
Considering the house-boat blend, there are (at least) two viable blends, “houseboat” and “boathouse”.
When considering, e.g., the pictures on the path between house and boat in Figure 5, it becomes clear
that it is not possible to place the boathouse reasonably on this path. It is thinkable of other betweenness
relations leading to the houseboat, however, as houseboat and boathouse are both based on totally
diferent generic spaces, it seems implausible that one of these could be considered as being in between
the other one and “house” or “boat” (e.g. not (ℎ, ℎ, )). Next to this example,
it also seems in general to be natural to assume, even based on one generic space, diferent paths from
one input to the other, respecting totally diferent facts of the input spaces.</p>
        <p>A visualization of the interpretation of conceptual blending as betweenness relation can be seen in
Figure 4 on the right. Two inputs, in this case “house” and “bottle” are considered and the generic space
is either explicitly (as done here) or implicitly determined. Then, instances of both house and bottle are
considered and between these instances, possible betweenness relations in form of paths are created.
These paths could be arbitrary shaped as long as they remain in the space of possible blends, thus the
region is restricted by the generic space and the consistency of the elements on the path. Based on the
optimality principles, it is then possible to determine good blends on the paths. Possible blends are, e.g.,
genie in a bottle or a house in a bottle in style of a ship in a bottle. Thereby it is possible that a path
does not contain any or contains several good blends.</p>
        <p>It is possible to apply the above considerations to given conceptual blending approaches, analyze
whether they are in line with these considerations and possibly proposing enhancements based on an
appropriate betweenness relation. This is done in the next section for visual blending which is, though
only a simplified version of conceptual blending, well interpretable with the help of a betweenness
relation and is a step towards conceptual blending with the help of betweenness.</p>
      </sec>
    </sec>
    <sec id="sec-4">
      <title>4. An Application to Visual Blending</title>
      <p>An area that lends itself to use in context with betweenness is when a geometric representation of the
objects is given, as those betweenness relations are widely studied and nicely applicable to examine the
underlying structure of such representation spaces. Such representations are given, e.g., in the area of
generative models. They are based on the idea that an input is mapped to a high-dimensional latent
space representation which is then mapped to an output. Examples are text-to-image models such as
stable difusion [21]. Without considering the technical details here, the basic idea is to give a short text
as input (e.g., “house”). This text is mapped to a vector representation in a high-dimensional latent space
out of which an image is generated. For a comprehensive overview of such techniques, see, e.g., [21].</p>
      <p>Such a latent space representation allows for considering betweenness of diferent representations,
especially, as the aim of such models is to represent not only the training data but to be able to create
new images based on the given ones which needs some sort of smoothness of the space.</p>
      <p>How could this space be used for doing some sort of blending? A straightforward approach to achieve
a visual blend is to combine the two inputs directly at text level, thus prompting, e.g., directly the
word “boathouse”. This could lead to reasonable results, especially for cases where the combined word
actually has the meaning the combination of words implies, such as “boathouse”. This has been done
by Ge and Parikh [22]. However, this does not necessarily lead to the desired results and especially
is no indicator of creativity. Consider, e.g., the blend of “butter” and “fly”. Whereas the combined
word “butterfly” has an assigned and well-known meaning independent of butter and fly, a visual blend
between butter and fly would be creative, e.g., a fly made out of butter.</p>
      <p>An approach based on text-to-image models that considers betweenness was presented by Melzi
et al. [23]. They implicitly considered betweenness by stating that something is a visual blend if it is in
between the representation of the two input texts in the latent space. First, for both inputs, the latent
space representation is created. Then, with the help of Euclidean betweenness, a point in between the
two is found and for this representation, an image is created.</p>
      <p>To improve this approach, it is possible to analyze the betweenness relation. As stated before,
Euclidean betweenness fulfills the betweenness axiom (C2) which is as discussed in Section 3.2 not
suitable for blending. Additionally, it is necessary to consider the underlying structure of the space
to find a betweenness that allows for a smooth interpolation between the two inputs and thus for a
path in between them. It has been observed, e.g., by Arvanitidis et al. [24] that the latent space is
non-linear, because of its non-linear generation. Alternative betweenness relations are, e.g., spherical
linear interpolation [25] or interpolation based on attention [26] for which an example can be seen in
Figure 5. This is, due to its importance to visual blending, a highly researched area with many proposed
interpolation functions from which the most can be interpreted as betweenness relations.</p>
      <p>This underlines the advantage of considering betweenness for blending, especially, but not limited
to geometric representations, as it allows for considering an order of elements that is not limited to
standard cases such as Euclidean betweenness. Therefore, such approaches are a good example why it
is helpful to consider abstract betweenness relations as conceptual blending approaches. Additionally,
the path-based view allows understanding the blending process and judging the quality of the blend
based on the smoothness of the path.</p>
      <p>However, these approaches still have some pitfalls. First, the approaches rely on the fact that there
are actually creative aspects represented in the latent space (and not only images which are part of
or similar to the training data) and, if such creative representations exist, they need to be actually
ifndable, thus in between the input representations based on the chosen betweenness relation. Next to
these technical problems, there are basic problems due to the fact that the blending is done solely on a
subsymbolic level, thus, conceptual information is not considered. By examining the example blend in
Figure 5, it can be seen that not only the boat is blended but also the background. From an open water
background in the first image, it is getting more and more hilly and forested in the course of the next
pictures. This is, however, an irrelevant information for the houseboat-blend. Therefore, it is necessary
to have a conceptual foundation of the blending and also of the betweenness relations, as until now,
these approaches achieve visual blends (thus combining images) but not visual conceptual blends [27],
thus the combination of images with the help of conceptual information.</p>
      <p>An option would be to consider two betweenness relations, one for the blend and one for the generic
space (the second version discussed in Section 3.2) and use the generic space-betweenness to guide the
blend betweenness. Another interesting option would be to generalize from this instance-based view of
these latent spaces to consider, e.g., sets of instances to define a blend on concept level. Such approaches
do, however, still not act on a conceptual level, as latent spaces do not, in general, incorporate conceptual
information. One option is to stick to betweenness on a latent space level but to equip the latent space
with some conceptual information, e.g., by modeling concepts as geometric objects in such spaces and
logical operations as geometric operations between them, e.g., with the help of spheres [28]. Another
option would be to actually consider the generic space on a symbolic and the blending betweenness on
a subsymbolic level, thus interpreting the conceptual blending process as a hybrid approach.</p>
      <p>However, note that this blending with latent spaces is only one application of the idea of doing
conceptual blending with the help of betweenness relations. Due to the nature of the latent space, it
invites to consider numerical betweenness relations which are widely studied and nicely applicable.
However, it is also possible to consider more abstract non-numeric betweenness relations, e.g.,
graphbased betweenness or variants of intersection betweenness (thus, following the first version discussed
in Section 3.2), to tackle other variants of conceptual blending in a betweenness-focused setting.</p>
    </sec>
    <sec id="sec-5">
      <title>5. Conclusion and Outlook</title>
      <p>The example of visual blending shows that interpreting blending as betweenness relation is worth a
try, as it helps to determine suitable properties of the blending and and enables to choose adequate
interpolation techniques. However, as the considerations on betweenness axioms showed, betweenness
is not only helpful for the visual blending case but can also be used to discuss conceptual blending
approaches in general. This leads to a number of interesting open questions: How could the betweenness
be considered in a setting that is not as geometric in nature as the visual blending case? How could
the two betweenness relations (of the blend and of the generic space) be combined? Also in the visual
blending setting further examinations are possible, namely, how to enhance the approach to not only
considering visual blending but actually visual conceptual blending?</p>
      <p>To conclude, in this paper, it has been shown that betweenness is an at least implicit image schematic
notion which can not only be used for spatio-temporal reasoning but also for abstract, metaphorical
considerations. These abstract notions can be used as a basic building block for creativity in the sense
of conceptual blending. Through its strong connection to embodied cognition, this approach seems to
be well justified and therefore worthwhile to be investigated further.</p>
    </sec>
    <sec id="sec-6">
      <title>Acknowledgments References</title>
      <p>We acknowledge the financial support through the ‘Abstractron’ project funded by the Autonome
Provinz Bozen - Südtirol (Autonomous Province of Bolzano-Bozen) through the Research Südtirol/Alto
Adige 2022 Call.</p>
    </sec>
  </body>
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