begin{filecontents}{jobname.bib}

@book{Chomsky1965,
    Address = {Cambridge Mass.},
    Author = {Noam Chomsky},
    Publisher = {{MIT} Press},
    Title = {Aspects of the Theory of Syntax},
    Year = {1965}}
end{filecontents}
documentclass{article}
usepackage{natbib}
setcitestyle{open={},close={}}
bibliographystyle{dcu}
begin{document}
citet{Chomsky1965}
bibliography{jobname}
end{document}