As Andrew Norman wrote, in a letter published in this book on page 113,  You flit freely back and forth between prescriptivism and descriptivism. 
( ( As ( ( Andrew Norman ) ( ( wrote , ) ( in ( ( a letter ) ( published ( in ( ( this book ) ( on ( page 113 ) ) ) ) ) ) ) ) ) ) ( , ( You ( ( ( flit ( freely ( ( back and ) forth ) ) ) ( between ( ( prescriptivism and ) descriptivism ) ) ) . ) ) ) )
(ROOT (S (SBAR (IN As) (S (NP (NNP Andrew) (NNP Norman)) (VP (VBD wrote) (, ,) (PP (IN in) (NP (NP (DT a) (NN letter)) (VP (VBN published) (PP (IN in) (NP (NP (DT this) (NN book)) (PP (IN on) (NP (NN page) (CD 113))))))))))) (, ,) (NP (PRP You)) (VP (VBP flit) (ADVP (RB freely) (RB back) (CC and) (RB forth)) (PP (IN between) (NP (NN prescriptivism) (CC and) (NN descriptivism)))) (. .)))
Prescriptivism and descriptivism cannot be juggled; pick one, says Andrew Norman in his letter.
( ( ( ( Prescriptivism and ) descriptivism ) ( ( can not ) ( ( ( be juggled ) ; ) ( pick one ) ) ) ) ( , ( ( says ( ( Andrew Norman ) ( in ( his letter ) ) ) ) . ) ) )
(ROOT (SINV (S (NP (NNP Prescriptivism) (CC and) (NNP descriptivism)) (VP (MD can) (RB not) (VP (VP (VB be) (VP (VBN juggled))) (: ;) (VP (VB pick) (NP (CD one)))))) (, ,) (VP (VBZ says)) (NP (NP (NNP Andrew) (NNP Norman)) (PP (IN in) (NP (PRP$ his) (NN letter)))) (. .)))