Accessing corpora: nltk.corpus : this is a Standardized interfaces to corpora and lexicons String processing nltk.tokenize, nltk.stem : Tokenizers, sentence tokenizers, stemmers Collocation discovery nltk.collocations: t-test, chi-squared, point-wise mutual information Part-of-speech tagging nltk.tag : n-gram, backoff, Brill, HMM, TnT Classification nltk.classify, nltk.cluster: Decision tree, maximum entropy, naive Bayes, EM, k-means Chunking nltk.chunk : Regular expression, n-gram, named entity Parsing nltk.parse : Chart, feature-based, unification, probabilistic, dependency . Semantic interpretation nltk.sem, nltk.inference : Lambda calculus, first-order logic, model checking Evaluation metrics nltk.metrics : Precision, recall, agreement coefficients Probability and estimation nltk.probability : Frequency distributions, smoothed probability distributions Applications nltk.app, nltk.chat : Graphical concordancer, parsers, WordNet browser, chatbo