I've updated the NLTK issue tracker with information about how the model for NLTK's built-in POS tagger was trained: https://github.com/nltk/nltk/issues/1063#is

I've updated the NLTK issue tracker with information about how the model for NLTK's built-in POS tagger was trained: https://github.com/nltk/nltk/issues/1063#issuecomment-138005116 https://github.com/nltk/nltk/issues/1063#issuecomment-138005... The second edition of the book will include a "scaling up" section in most chapters, which shows how to transition from NLTK's pure Python implementations to NLTK's wrappers for the Stanford tools.