they have a tendency to slip into hokum 
(ROOT (S (NP (PRP they)) (VP (VBP have) (NP (DT a) (NN tendency) (S (VP (TO to) (VP (VB slip) (PP (IN into) (NP (NN hokum))))))))))
(ROOT (S (NP (PRP )) (VP (VBP ) (NP (DT ) (NN ) (S (VP (TO ) (VP (VB ) (PP (IN ) (NP (NN ))))))))))