In Chapter 6, Holmes must contend with the incompetent Athelney Jones, a local policeman whose shoddy intuition about Bartholomew's murder hinders Holmes's own investigation into the crime. As Holmes disparages Jones to Watson (and the reader), he lets loose two literary allusions—one in French, one in German:
'He can find something,' remarked Holmes, shurgging his shoulders; 'he has occasional glimmerings of reason. Il n'y a pas des sots si incommodes que ceux qui on de l'esprit?'
This first quotation is from Les Maximes, a collection of maxims published by the French aristocrat François de La Rochefoucauld in 1665. This particular maxim reads, "there are no fools so troublesome as those who have some wit." Evidently, Holmes finds Jones to be just bright enough to be irritating but not bright enough to draw any real conclusions about Bartholomew's death.
Holmes closes the chapter with another allusion, which is also an example of verbal irony:
Then I shall study the great Jones's methods and listen to his not too delicate sarcasms.
Wir sind gewohnt dass die Menschen werhöhnen was sie nicht verstehen.
'Goethe is always pithy.'
This second reference is from the first part of Johan Wolfgang von Goethe's legendary play, Faust: "We are used to seeing that man despises what he never comprehends." Evidently, Holmes does not find Jones to be "great" at all—this is an example of his withering verbal irony. Rather, Holmes sees Jones's suspicion about his detective work to be proof of Jones's own stupidity.
Holmes's penchant for such allusion and facile use of multiple languages underscore his fierce intelligence and his fierce belief in the power of knowledge and reason. Both of these quotes warn of the dangers brought by the uninformed.