Returns an list of tuples of the form (word, POS tag).
    Example:
    ::
        [('At', 'ADP'), ('eight', 'NUM'), ("o'clock", 'NOUN'), ('on', 'ADP'),
        ('Thursday', 'NOUN'), ('morning', 'NOUN')]
    :rtype: list of tuples

def pos_tags(self):
    """Returns an list of tuples of the form (word, POS tag).
    Example:
    ::
        [('At', 'ADP'), ('eight', 'NUM'), ("o'clock", 'NOUN'), ('on', 'ADP'),
        ('Thursday', 'NOUN'), ('morning', 'NOUN')]
    :rtype: list of tuples
    """
    tagged_words = []
    for word,t in self.pos_tagger.annotate(self.words):
      word.pos_tag = t
      tagged_words.append((word, t))
    return tagged_words