'Adds a new Word to the sentence.
Other Sentence._do_[tag] functions assume a new word has just been appended.'

def _do_word(self, word, lemma=None, type=None):

    if ((lemma == "'s") and (type in ('VB', 'VBZ'))):
        lemma = 'be'
    self.words.append(Word(self, word, lemma, type, index=len(self.words)))
