Any viable rule of analogicalinference would need to be supplemented with considerations of relevance that depend on subject matter, historical context, and logical details particular to each analogical argument
Viable(describing whether a rule can actually function well)
Capable of working or being practical in real situations; feasible and effective.
relevance(The simplest notion is containment of query terms; more refined notions weight terms by distinctiveness via tf-idf)
The degree to which a document addresses or is pertinent to a given query or topic
subject matter(Contrasted with Platonic forms to establish a historically situated ontology of artistic content)
That which transcends individual artworks yet does not exist apart from its historical embodiments; unlike Platonic forms, subject matters mutate and develop through history
To generalize the difficulty: not every similarity increases the probability of the conclusion and not every difference decreases it. Some similarities and differences are known to be (or accepted as being) utterly irrelevant and should have no influence whatsoever on our probability judgments. To be viable, rule (5) would need to be supplemented with considerations of relevance, which depend upon the subject matter, historical context and logical details particular to each analogical argument.