A HYBRID MODEL OF REASONING BY ANALOGY

when the activation of some node exceeds a given threshold.
The model presented in this chapter also uses the notion of spreading activation. The proposed
variation is in some aspects closer to Anderson's ideas (it has an automatic nature) and in others to
Holyoak and Thagard's work (the analogical mapping is triggered by the change of the focus, i.e.
by the change of a node's activation). What is different from both approaches is that spreading
activation is considered neither as an instantaneous operation before some matching processes
start, nor as a side effect of the reasoning itself. Instead, this process runs continuously and in
parallel to all other reasoning processes and thus influence their work reflecting the changing
environment.
7.2.2. Mapping
The foremost problem with mapping, how to overcome the combinatorial explosion which will
take place in case of an exhaustive comparison between all possible correspondences, is solved in
various ways by various researchers.
Gentner (1983), Falkenhainer et al. (1986) in their structure mapping theory (SMT) restrict
possible element correspondences only to identical relations (attributes are discarded, objects are
put in correspondence after the best mapping is found) and use a purely syntactic criterion for
preference - the systematicity principle: it is the higher-order relational structure that determines
which of two possible matches is made, preferring systems of predicates that contain higher-order
relations (a syntactic expression of the tacit preference for coherence and inferential power in
analogy). There are several problems with this approach. First, there are a lot of cases where
different relations have to be put in correspondence (e.g. on(A, B) - support(B, A), on(A, B) - intouch(A,
B), etc.). Second, object attributes are sometimes quite relevant (e.g. it is the attribute
hot(plate) that causes the water to be heated). Third, this single criterion could be insufficient if, for
example, two or more higher-order relations exist and the corresponding relational structures are
equally systematic. Moreover, there are cases where the more systematic relational structure is less
relevant and has to be ignored.
Keane (1988) follows a radical pragmatic approach. According to what he proposes, the first stage
of the reasoning process finds the critical object(s) of the target's goal (i.e. the object(s) whose
manipulation or use is necessary to the achievement of the goal) and their functionally relevant
attributes (FRAs). (The FRAs are those attributes which became salient in the context of a
particular goal; one possible operationalization of this idea (Kedar-Cabelli, 1988) is the building of
an explanation network.) Next, the reasoning process looks for an object with the same or similar
FRA in the source domain and the relations which predicate this critical object in the source are
mapped. Finally, other relations are mapped following the "cause" relations.
This approach will also cause problems in several cases. First, as Gentner would say, this
approach is restricted to problem solving where a clear goal exists. Second, it is not always
possible to define a critical object and its FRA in the target situation before knowing the plan for
achieving the goal; if, however, the plan is known, such an analogy would be used only for plan
repairing. Third, in complex situations it would be necessary to use some kind of structural
constraints in order to decide which of the relations predicating the critical object should be
mapped.
That is why I follow the approach proposed by Holyoak and Thagard (1989b) and use the
structural, semantic, and pragmatic constraints together. However, the mechanism for mapping is
extended significantly so that a constraint satisfaction machine similar to ACME will be only a part
of the whole mapping process. The mechanisms for construction of the network are elaborated,