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A Beginner’s Guide to Part of Speech Tagging in NLP

Part-of-speech (POS) tagging is a fundamental task in Natural Language Processing (NLP). It refers to the process of assigning a part-of-speech tag to each word in a sentence, such as noun, verb, adjective, or adverb.

The information about the part-of-speech tag of each word is significant for various NLP applications, such as entity recognition, sentiment analysis, machine translation, and many more. By applying Part-of-speech tagging to a sentence, we can understand the grammatical structure, the interpretation of meaning in a better way.

Basics of Part-of-Speech Tagging

Definition of Part-of-Speech Tagging

Part-of-Speech tagging is a form of syntactic annotation in which words are assigned one of the parts of speech based on their syntactic and contextual usage. It is done by analyzing and identifying the context in which a word is used in a sentence.

For example, if the word “run” is used in a sentence, “I run every morning,” then it is assigned a verb tag. Similarly, “important” is assigned an adjective tag in the sentence, “This is an important matter.”

Importance of Part-of-Speech Tagging in NLP

Part-of-speech tagging is a necessary and significant step in NLP. It helps in building a better understanding of the meaning and structure of sentences.

The information provided by the POS tag can improve the performance of many NLP applications, such as automated text summarization, named entity recognition, and sentiment analysis.

The POS tag helps to resolve the ambiguity problem that arises in sentences with multiple meanings, depending on which words are assigned specific parts of speech. Overall, Part-of-Speech Tagging is important in NLP and helps to improve the accuracy of various applications significantly.

Parts of Speech

Part-of-Speech Tagging divides text into categories based on the role that words play in a sentence. Each word belongs to a grammatical category called the Parts of Speech (POS). There are eight parts of speech that a word can belong to:


A Noun is a word that is used to refer to people, things, places, or concepts, etc. For example, “dog,” “London,” “happiness,” and “ideas” are all nouns.


The Verb is the action or state of being in the sentence. It refers to the action or occurrence of an event. For example, “run,” “play,” and “work” are all verbs.


An Adjective is a word that describes or modifies a noun or pronoun. It provides additional information about the noun or pronoun to which it relates. For example, “beautiful,” “red,” and “happy” are all adjectives.


An Adverb is a word that describes or modifies a verb, adjective, or another adverb. It provides additional information about the verb, adjective, or adverb to which it relates. For example, “quickly,” “very,” and “often” are all adverbs.


A Pronoun is a word that is used in the place of a noun. It replaces a noun that has already been mentioned. For example, “he,” “she,” “it,” and “they” are all pronouns.


A Preposition is a word that shows the relationship between a noun/pronoun and other words in the sentence. For example, “in,” “on,” “above,” and “under” are all prepositions.


A Conjunction is a word that connects words, phrases, or clauses. It helps to join the sentence parts, and provide structure and logic to the sentence. For example, “and,” “but,” and “or” are all conjunctions.


An Interjection is a word that is used to express an emotion or a feeling abruptly. It is often used to convey surprise, joy, or pain. For example, “Wow!”, “ouch,” and “alas” are all interjections.

Techniques for Part-of-Speech Tagging

There are various techniques to perform Part-of-Speech Tagging, each with its strengths and weaknesses. Here are three common approaches:

Rule-Based Approach

The Rule-Based approach involves creating grammatical rules and applying them to Part-of-Speech Tagging.

It involves developing a set of rules based on the syntactic and contextual information of each word. It is also called a deterministic approach since it involves a fixed set of predetermined rules to categorize words.

The advantage of the rule-based approach is that it is transparent, interpretable, and easily explainable. A disadvantage of this approach is that it may produce inconsistent results when it faces difficult linguistic phenomena.

Stochastic Approach

The Stochastic approach, also known as a statistical approach, involves using statistical models to predict the Part-of-Speech of each word. It involves analyzing the patterns in a large corpus of tagged text and learning the probabilities of each word being assigned a particular Part-of-Speech tag.

The advantage of the Stochastic approach is that it is scalable to large datasets, and it can provide probabilistic measures for each tag. A disadvantage of this approach is that it may not account for specific types of language or vocabulary that were not present in the original corpus.

Hybrid Approach

The Hybrid Approach combines the advantages of the Rule-Based and Stochastic approaches. This approach aims to reduce the drawbacks of both techniques by combining them. It helps to improve the accuracy of Part-of-Speech Tagging by integrating the rules-based approach with statistical models.

The Hybrid approach automatically learns the patterns in tagged data and also considers explicit rules for tagging. The Hybrid approach has a higher degree of accuracy compared to the other two methods. However, it may be less interpretable than the rule-based approach.

Challenges in Part-of-Speech Tagging

Although Part-of-Speech Tagging is a fundamental task in NLP, it is also challenging due to several difficulties. Here are four challenges in Part-of-Speech Tagging:


One of the main challenges in Part-of-Speech Tagging is the ambiguity of some words of the context. They can have different meanings based on the surrounding words. Resolving the ambiguity problem is a crucial step to improve the accuracy of the Part-of-Speech Tagging.

Out of Vocabulary Words

The size of vocabulary in natural language is vast, and new words are continually being added. Part-of-Speech taggers rely on lexicons or dictionaries, which contain a predefined set of words; however, they may not be aware of previously unseen words.

Identifying out-of-vocabulary words is necessary to avoid errors in the tagging process.

Inconsistent word usage

The inconsistent usage of words can further complicate Part-of-Speech Tagging. Words can be used differently in different contexts, making it challenging to assign the appropriate Part-of-Speech tag.

The inconsistencies in spelling, syntax, and usage of language make it difficult for taggers to produce accurate results.

Multilingual Tagging

Multilingual tagging is a more challenging task than tagging in a single language. The structure and grammar of each language differ, and Part-of-Speech Tagging requires a deeper understanding of the specific language.

In a multilingual context, there may be words with the same spelling but different meanings that require different tags. This makes it challenging to develop effective Part-of-Speech Tagging algorithms.

Applications of Part-of-Speech Tagging

The Part-of-Speech Tagging technique has a wide range of applications in NLP. Here are some of the major applications:

Sentiment Analysis

Sentiment Analysis is the process of determining the positivity or negativity of a piece of text. Part-of-Speech Tagging is useful in Sentiment Analysis to extract relevant information to determine the sentiment of a word or phrase.

By analyzing the parts of speech of words, such as adjectives or verbs, Sentiment Analysis algorithms can identify the sentiment expressed in each sentence.

Named Entity Recognition

Named Entity Recognition (NER) is the process of identifying and classifying real-world objects, such as persons, organizations, and locations, in text.

Part-Of-Speech Tagging is used in NER to identify and extract entities. For instance, in the sentence, “I visited New York last year,” the system would recognize “New York” as a location.

Machine Translation

Machine Translation is the process of translating text from one language to another language.

Part-of-Speech Tagging has an essential role in Machine Translation because it assists in identifying the grammatical structure of a sentence in the original language, which helps in generating its equivalent translation.

By providing accurate parts of speech tags to words, it helps in making the translation more accurate.

Text-to-Speech Conversion

Part-of-Speech Tagging is used in Text-to-Speech (TTS) Conversion to generate human-like speech. By understanding the parts of speech tags of the words, the TTS system produces intonation and stress in speech, which helps in generating more natural-sounding voices.

Information Retrieval

Information Retrieval is the process of searching through a large amount of data to extract relevant information from it. Part-of-Speech Tagging is used in Information Retrieval to improve the accuracy of search results.

For instance, a search engine can use Part-of-Speech Tagging to understand whether a user’s search query is asking for a definition of a particular word or asking for information about an individual or entity.


Part-of-Speech Tagging is an essential technique in Natural Language Processing (NLP) that is used to identify the part of speech of each word in a sentence.

It helps to understand the grammatical structure of a sentence and improves the performance of various NLP applications, such as Sentiment Analysis, Named Entity Recognition, Machine Translation, Text-to-Speech Conversion, and Information Retrieval.

Summary of Part-of-Speech Tagging in NLP

This article has described the definition, importance, and applications of Part-of-Speech Tagging. It has discussed the types of Parts of Speech, techniques, and challenges in Part-of-Speech tagging.

The article highlights that Part-of-Speech Tagging is a fundamental task in NLP and improves the accuracy of various applications by providing context-specific information.

Future scope and advancements in Part-of-Speech Tagging

The advancements in NLP are constantly improving Part-of-Speech Tagging. The future scope of Part-of-Speech Tagging includes the development of hybrid approaches that combine the strengths of the different techniques.

It also involves the use of deep learning techniques like Recurrent Neural Networks and Convolutional Neural Networks to tag Part-of-Speech.

These techniques have the potential to improve the accuracy and efficiency of Part-of-Speech Tagging, making it easier for machine learning algorithms to understand natural language.

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