In transformational grammar the notion of a chain has been central ever sin
ce its introduction in the early 80s. However, an insightful theory of chai
ns has hitherto been missing. This paper develops such a theory of chains.
Though it is applicable to virtually all chains, we shall focus on movement
-induced chains. It will become apparent that chains are far from innocuous
. A proper formulation of the structures and algorithms involved is quite a
demanding task. Furthermore, we shall show that it is possible to define s
tructures in which the notion of a chain coincides with that of a constitue
nt, so that the notion of a chain becomes redundant, generally without maki
ng the theory more complicated. These structures avoid some of the problems
that beset the standard structures (such as unbound traces created by remn
ant movement).