The behaviour and lexical quality of the folksonomies is examined by comparing two online social networks: LibraryThing (for books) and Flickr (for photos). We presented a case study that combines quantitative and qualitative elements, singularized by the lexical and functional framework. Our query was made by "Legal History" and by the synonyms "Law History" and "History of Law." We then examined the relevance, consistency and precision of the tags attached to the retrieved documents, in addition to their lexical composition. We identified the difficulties caused by free tagging and some of the folksonomy solutions that have been found to solve them. The results are presented in comparative tables, giving special attention to related tags within each retrieved document. Although the number of ambiguous or inconsistent tags is not very large, these do nevertheless represent the most obvious problem to search and retrieval in folksonomies. Relevance is high when the terms are assigned by especially competent taggers. Even with less expert taggers, ambiguity is often successfully corrected by contextualizing the concepts within related tags. A propinquity to associative and taxonomic lexical semantic knowledge is reached via contextual relationships.