English Part-of-Speech Tagging in Flair (default model)

This is the standard part-of-speech tagging model for English that ships with Flair.

F1-Score: 98,19 (Ontonotes)

Predicts fine-grained POS tags:

tag meaning
ADD Email
AFX Affix
CC Coordinating conjunction
CD Cardinal number
DT Determiner
EX Existential there
FW Foreign word
HYPH Hyphen
IN Preposition or subordinating conjunction
JJ Adjective
JJR Adjective, comparative
JJS Adjective, superlative
LS List item marker
MD Modal
NFP Superfluous punctuation
NN Noun, singular or mass
NNP Proper noun, singular
NNPS Proper noun, plural
NNS Noun, plural
PDT Predeterminer
POS Possessive ending
PRP Personal pronoun
PRP$ Possessive pronoun
RB Adverb
RBR Adverb, comparative
RBS Adverb, superlative
RP Particle
SYM Symbol
TO to
UH Interjection
VB Verb, base form
VBD Verb, past tense
VBG Verb, gerund or present participle
VBN Verb, past participle
VBP Verb, non-3rd person singular present
VBZ Verb, 3rd person singular present
WDT Wh-determiner
WP Wh-pronoun
WP$ Possessive wh-pronoun
WRB Wh-adverb
XX Unknown

Based on Flair embeddings and LSTM-CRF.

Demo: How to use in Flair

Requires: Flair (pip install flair)

from flair.data import Sentence
from flair.models import SequenceTagger

# load tagger
tagger = SequenceTagger.load("flair/pos-english")

# make example sentence
sentence = Sentence("I love Berlin.")

# predict NER tags

# print sentence

# print predicted NER spans
print('The following NER tags are found:')
# iterate over entities and print
for entity in sentence.get_spans('pos'):

This yields the following output:

Span [1]: "I"   [− Labels: PRP (1.0)]
Span [2]: "love"   [− Labels: VBP (1.0)]
Span [3]: "Berlin"   [− Labels: NNP (0.9999)]
Span [4]: "."   [− Labels: . (1.0)]

So, the word "I" is labeled as a pronoun (PRP), "love" is labeled as a verb (VBP) and "Berlin" is labeled as a proper noun (NNP) in the sentence "I love Berlin".

Training: Script to train this model

The following Flair script was used to train this model:

from flair.data import Corpus
from flair.datasets import ColumnCorpus
from flair.embeddings import WordEmbeddings, StackedEmbeddings, FlairEmbeddings

# 1. load the corpus (Ontonotes does not ship with Flair, you need to download and reformat into a column format yourself)
corpus: Corpus = ColumnCorpus(
                column_format={0: "text", 1: "pos", 2: "upos", 3: "ner"},

# 2. what tag do we want to predict?
tag_type = 'pos'

# 3. make the tag dictionary from the corpus
tag_dictionary = corpus.make_tag_dictionary(tag_type=tag_type)

# 4. initialize each embedding we use
embedding_types = [

    # contextual string embeddings, forward

    # contextual string embeddings, backward

# embedding stack consists of Flair and GloVe embeddings
embeddings = StackedEmbeddings(embeddings=embedding_types)

# 5. initialize sequence tagger
from flair.models import SequenceTagger

tagger = SequenceTagger(hidden_size=256,

# 6. initialize trainer
from flair.trainers import ModelTrainer

trainer = ModelTrainer(tagger, corpus)

# 7. run training


Please cite the following paper when using this model.

  title={Contextual String Embeddings for Sequence Labeling},
  author={Akbik, Alan and Blythe, Duncan and Vollgraf, Roland},
  booktitle = {{COLING} 2018, 27th International Conference on Computational Linguistics},
  pages     = {1638--1649},
  year      = {2018}


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