provides an invaluable service by sparking debate and encouraging thought 
(ROOT (S (VP (VBZ provides) (NP (DT an) (JJ invaluable) (NN service)) (PP (IN by) (S (VP (VP (VBG sparking) (NP (NN debate))) (CC and) (VP (VBG encouraging) (NP (NN thought)))))))))
(ROOT (S (VP (VBZ ) (NP (DT ) (JJ ) (NN )) (PP (IN ) (S (VP (VP (VBG ) (NP (NN ))) (CC ) (VP (VBG ) (NP (NN )))))))))