by sparking debate and encouraging thought 
(ROOT (PP (IN by) (S (VP (VP (VBG sparking) (NP (NN debate))) (CC and) (VP (VBG encouraging) (NP (NN thought)))))))
(ROOT (PP (IN ) (S (VP (VP (VBG ) (NP (NN ))) (CC ) (VP (VBG ) (NP (NN )))))))