Flexibility in symmetry: An implicational relation in Bantu double object constructions

This paper presents new data from Bantu languages, from which a hitherto unnoticed typological pattern emerges: A) language-internally, causative, applicative and lexical (‘give’) ditransitives can differ with respect to symmetry; B) crosslinguistically, they are in an implicational relationship: if a language is symmetrical for one type of predicate, it is symmetrical for the predicate types to its right as well:
 
causative >  applicative > lexical ditransitive
 
This can be accounted for if symmetry is due to low functional heads being flexible to license an argument in either their complement or their specifier  \citep{HaddicanHolmberg2012,HaddicanHolmberg2015}. This flexibility is argued to be a sensitivity to topicality. The implicational relation can then be seen as a requirement for lower functional heads to have the same sensitivity: if Caus can license its specifier, then HAppl and LAppl should also be able to do so.