Tautologies are among the prime examples to demonstrate the contribution of pragmatic principles to the interpretation of utterances that would be uninformative from a strictly logical and truth-conditional perspective. While traditionally the focus has been on nominal tautologies (a is a), the present paper is concerned with the hitherto lesser-studied subtype of headless relatives (what p, p). On the example of German wer kann, der kann (lit.: ‘he who can, can’) it will be illustrated how semantics (polysemy of können ‘can’), syntax (correlative free relative clause) and pragmatics (Q- and R-principles) interact to yield the specific communicative effects associated with this tautology. Exhibiting one-to-one correspondences (in lexical, structural and functional terms) in some languages, such as Slovene, but not in others, such as Russian and English, wer kann, der kann at the same time serves as a test case for the ‘radically pragmatic’ and ‘radically semantic’ approaches to tautologies.