As part of the Theme extraction Ipiphany uses semantic processing, which determines how related or similar the specific words or word associations are.
E.g. fix ~ resolve
However, this technology is not perfect and there are a number of challenges presented by the complexity of language:
The same word can have multiple meanings and be used in different ways e.g. fix=repair and fix=to stick
Words can have very broad usages – this is especially the case for verbs e.g. understand ~ remember ~ explain ~ feel ~ see