English words have been traditionally classified into eight lexical categories, or parts of speech (and are still done so in most dictionaries):
• Noun: any abstract or concrete entity
• Pronoun: any substitute for a noun or noun phrase
• Adjective: any qualifier of a noun
• Verb: any action or state of being
• Adverb: any qualifier of an adjective, verb, or other adverb
• Preposition: any establisher of relation and syntactic context
• Conjunction: any syntactic connector
• Interjection: any emotional greeting (or "exclamation")
Although these are the traditional eight English parts of speech, modern linguists have been able to classify English words into even more specific categories and sub-categories based on function.
The four main parts of speech in English, namely nouns, verbs, adjectives and adverbs, are labelled form classes as well. This is because prototypical members of each class share the ability to change their form by accepting derivational or inflectional morphemes. The term form is used as it refers literally to the similarities in shape of the word in its pronunciation and spelling for each part of speech.
Neither written nor spoken English generally marks words as belonging to one part of speech or another, as they tend to be understood in the context of the sentence. Words like neigh, break, outlaw, laser, microwave and telephone might all be either verb forms or nouns. Although -ly is a frequent adverb marker, not all adverbs end in -ly (-wise is another common adverb marker) and not all words ending in -ly are adverbs. For instance, tomorrow, fast, very can all be adverbs, while early, friendly, ugly are all adjectives (though early can also function as an adverb).
In certain circumstances, even words with primarily grammatical functions can be used as verbs or nouns, as in "We must look to the hows and not just the whys" or "Miranda was to-ing and fro-ing and not paying attention".
Functional classification
The study of linguistics has expanded the understanding of lexical categories in various languages and allowed for better classifying words by function. Common lexical categories in English by function may include:
1. Open word classes:
o adjectives
o adverbs
o nouns
o verbs (except auxiliary verbs)
o Interjections
2. Closed word classes:
o auxiliary verbs
o clitics
o coverbs
o conjunctions
o determiners (articles, quantifiers, demonstrative adjectives, and possessive adjectives)
o particles
o measure words
o adpositions (prepositions, postpositions, and circumpositions)
o preverbs
o pronouns
o contractions
o cardinal numbers
