If you studied traditional grammar in school, you probably recall learning about the eight parts of speech: nouns, verbs, adjectives, adverbs, pronouns, prepositions, conjunctions, and interjections. Early English grammarians adapted these categories from those of classical Greek and Latin, and for centuries the parts of speech were introduced to students--in the words of the anonymous author of The English Accidence (1733)--as "the foundation upon which the beautiful fabrick of the language stands."

Yet for most of the past century, notes David Crystal, linguists have regarded the parts of speech as little more than "convenient fictions."

For instance, in A Comprehensive Grammar of the English Language (Longman, 1985), Randolph Quirk expresses a strong preference for the term (and the concept) word class. According to Quirk and his colleagues, "The names of the parts of speech are traditional, and neither in themselves nor in relation to each other do these names give a safe guide to their meaning, which instead is best understood in terms of their grammatical properties."

Likewise, in the authoritative Cambridge Grammar of the English Language (2002), the term parts of speech shows up just once in the opening chapter, and in the next 1,800 pages is never seen again: "Any theory of syntax of the general sort we provide, and most types of dictionary, must include a list of the lexical categories or parts of speech assumed."

And in Ronald Carter and Michael McCarthy's Cambridge Grammar of English: A Comprehensive Guide (2006), only a single reference to the parts of speech appears in its nearly 1,000 pages: "Word classes are traditionally called parts of speech."

The parts of speech haven't disappeared, of course, but they have been reconsidered, reorganized, and (in some cases) renamed. (You'll have to admit that after 2,000 years some changes were overdue.) The alternative terms favored by most contemporary linguists are lexical categories, syntactic categories, and, as we've seen, word classes (a term introduced in the first half of the 20th century).

So is there universal agreement on the number, make-up, and nature of these word classes? Not at all. But if you're looking for an up-to-date system of lexical typology that's approachable, teachable, and somewhat familiar, I recommend the one adopted by Martha Kolln and Robert Funk in Understanding English Grammar (Longman, 2011):

FORM CLASSES (also known ascontent words or open classes)
Nouns
Verbs
Adjectives
Adverbs

STRUCTURE CLASSES (also known asfunction words or closed classes)
Determiners
Pronouns
Auxiliaries
Conjunctions (orConjuncts)
Qualifiers
Interrogatives
Prepositions
Expletives
Particles

"In general," say Kolln and Funk, "the form classes provide the primary lexical content; the structure classes explain the grammatical or structural relationship. We can think of the form-class words as the bricks of the language and the structure words as the mortar that holds them together."
 

Then again, if you're averse to change or just feeling nostalgic for the way grammar was taught in Mrs. Grundy's English class, you can always visit What Are the Parts of Speech?
 

More About English Grammar: Word Classes and the Parts of Speech

• Closed Classes and Open Classes
• Cobbett's Advice on Studying Grammar
• Content Words and Function Words
• Grammatical Categories and Grammatical Functions
• "Sir Hornbook," a Grammatical Ballad by Thomas Love Peacock
• "The Teaching of English Grammar," by Oliver Farrar Emerson
• Ten Types of Grammar: Different Ways of Analyzing the Structures and Functions of Language
• What Are the Parts of Speech?