Madden was the leading palaeographer of his day. However, his ignorance of German prevented his ranking high as a philologist, although he paid much attention to the early dialectical forms of French and English. His minor contributions to antiquarian research were numerous: the best known, perhaps, was his dissertation on the spelling of Shakespeare's name, which, mainly on the strength of a signature found in John Florio's copy of the work of Montaigne, he contended should be "Shakspere."