What is a part of speech? You might not believe how much disagreement and nuanced analysis surrounds that question.
This essay ventures into some philosophical questions—What does it mean to classify a word, and how and why have those classifications changed?—before emerging with a bit of writerly advice. I find this excursion invigorating, like a deep‑sea search for treasure. Come along, and we’ll share the spoils.
According to one modern school of linguistic thought, only four word types—nouns, verbs, adjectives, and adverbs—now qualify as parts of speech. Four. The nerve! These, the parts of speech (also called form‑class words, as we’ll explore deeper down) comprise “the vast majority of words in the English language.” The other word types traditionally considered parts of speech—prepositions, pronouns, conjunctions, and interjections (give or take a part)—no longer belong to the club.
Sounds crazy at first. But looking at word types in this new way makes sense, and it solves a problem. The problem with the traditional, more‑inclusive parts‑of‑speech classification scheme, which remains in common use, is the schizophrenic way it defines word types: “sometimes on meaning, sometimes on function.” Is take a noun? The traditional take on parts of speech—the old classification scheme—lacks the distinctions required for answering this question precisely. Maybe. Sometimes. It depends. We need a better way to talk about words: a better metalanguage.
The modern take gives us a better metalanguage. That metalanguage hinges on new distinctions related to form and function.
What do form and function mean when it comes to words? All linguists, traditional and modern, agree on this answer.
- A word’s form is its “physical shape.” Form is “what we see or hear when someone uses a word.” The form of the word sidewalk is s‑i‑d‑e‑w‑a‑l‑k. If you add or delete or change the letters—whether meaningfully (sidewalks) or randomly (sidewalkqwerty or qwertysidewalk or sdqwertywks)—you change its form.
- A word’s function is the grammatical role it plays in a phrase or sentence. Sidewalk plays one role in Let’s shovel this sidewalk and another in I’ve got the sidewalk blues.
Notice that we haven’t yet asked what kind of word sidewalk is; we haven’t yet attempted to classify this word. We’re setting up a framework for classifying words. (Keep your oxygen flowing. The world we’re descending into is esoteric if also wondrous.)
In this crazy language that is English, when you get a hankering to classify a word, you have to look at both its form and its function: the word in itself and the word in the context of other words around it. For example, in Call me a shoveling fool, the word shoveling is a verb in form (it ends in –ing) and an adjective in function (it modifies the noun fool). The reality that “form and function do not always match in English” has been called “the despair of grammar students.” But we’re stuck with it. Coming to terms with the form-function duality—understanding that Is take a noun? is a two-part question—“is essential for comprehending how English works.”
(It’s also essential for enjoying the New York Times crossword puzzle.)
In a sense, sometimes, you can identify a word “by default”(as a noun, adjective, conjunction, or what have you) just by looking at its form in isolation. Sidewalk, for instance, can be called a noun “in form.”
How can we say that? This turns out to be a good question. Answering it, if you’re a discerning linguist, requires invoking tests for nounness that go beyond the person-place-or-thing definition. Here’s one test: Does adding an s create a plural in natural usage? (Yes, sidewalks is a perfectly pedestrian plural. One point for nounness.) A couple of similar tests later, and you have enough clues to determine not only whether a word is a noun in form but how nouny it is. Nounness, it turns out, has a continuum. A noun may be true to form in all ways or in only some ways.
Linguists apply tests to single words (they look for “features of form”) the way chemists apply “a series of chemical tests to identify an unknown substance.” They have tests for all four types of form-class words, those newly narrowed parts of speech: nouns, verbs, adjectives, and adverbs. For our purposes, which include not drowning, we need to know only this: the form-class foursome have something in common that differentiates them from the erstwhile parts of speech. The differentiator? At the risk of oversimplifying—stay away from the derivational and inflectional morphemes!—I’ll put it this way: form-class words can change form in predictable ways and still make sense. If you tack on an s, an ing, or an est at the end, or a pre or an ultra at the beginning, you get words that you’d find in a dictionary. Sidewalk becomes sidewalks. Shovel becomes shoveling. Cold becomes ultracold. No one so much as blinks.
The ex–parts of speech? No can do. Take a preposition (of), a pronoun (it), or a conjunction (and). If you change the form of these words in the usual ways (ofing, itest, ultraand), you get something that Merriam-Webster won’t go near. In natural usage, these words have one form only.
Since these ex-parts of speech, unlike the now-parts, have only one natural form, it would make no sense to tack on a prefix or suffix to test a word for, say, prepositionness or pronounness. A given word, like from or she, might usually act as a preposition or as a pronoun, and so we often comfortably (unthinkingly) apply these labels. We jump to classification based on form alone. But in these cases, from a linguist-as-chemist point of view, the word itself gives nothing away. These words have no “features of form” to test against. Calling a word a “preposition in form” or “pronoun in form” would have no meaning. We can’t call any word of this type “true to form.”
What else makes the ex-parts unique? Whereas form-class words (also called content words: tree, run, fabulous, dizzily) contain “lexical meaning” in themselves, the ex–parts (of, it, and) contribute “grammatical meaning” to a sentence.
To acknowledge the uniqueness of these ex-parts—of all word types that lack parts-of-speechness—modern linguists give them a club of their own: the structure class. If form-class words are parts of speech, structure-class words are connectors of parts of speech.
Structure-class words, or structure words, hold sentences together and enable them to make sense. Structure words may have no “features of form,” but oh, baby, do they have features of function—so much so that they’re also called function words. They are all about what they do. They have one and only one reason to get out of bed every morning: to create relationships between other words. They are the matchmakers of the sentence world. These words put the diagram in sentence diagram. Only the most rudimentary of sentences could exist (See John jump) without structure words.
For the record, structure words include prepositions (with), pronouns (he), conjunctions (but), determiners (the), auxiliaries (might), qualifiers (very), relatives (whose), and interrogatives (where).
From is a structure word in this sentence: Call me a shoveling fool from Liverpool. It does what only a preposition can do: it creates a relationship between its object (Liverpool) and another noun (fool). Without structure-class words, like from, to bring coherence to the jumbo jumble of form-class words—that plenitudinous stockpile of disconnected speech parts—you and I couldn’t be communing right now because books would not exist. Isn’t it time that words this uniquely and powerfully endowed had a class of their own?
Compared with the monocular traditional view of parts of speech, the binocular modern take, with its distinction between form-class and structure-class words, gives us a more accurate and useful way to communicate, and think, about these multidimensional critters known as words. The new metalanguage provides a more meaningful peek into the way language works.
What’s more—here we emerge from the sea with gold in hand—this distinction between form-class and structure-class words gives writers new insight into an ancient tool for enlivening sentences, a tool that yields “instances of wonderfully imaginative language use.” The tool goes by various names, including anthimeria (with or without the h), grammatical shift, and enallage. These terms all get at the same thing: the twisting of a word’s expected usage—the yanking of words out of what linguists call their “natural classes.”
You can accomplish this twisty yankiness in two ways:
- Add a prefix or suffix, thereby changing the word’s form (parts-of-speechness).
- Plug the word into a mind-pricklingly surprising position in a sentence, thereby changing its function (On the count of three, everybody enallage).
Arthur Plotnik, who writes lively books on lively writing, gives this playful example: “So how can questy writers enallage their way to the big Fresh? On that little how, we could noun and verb you all day.”
How does the distinction between form-class and structure-class words ratchet up our enallagitudinous abilities? It points us straight to the pay-off words: the form-class words. Words of these types (donut, bristle, cheeky, abundantly), with their continua of form, afford the most play. A glance at Lewis Carroll’s famous poem “Jabberwocky” (All mimsy were the borogoves, And the mome raths outgrabe) snapdoodles this point home.
When you need an especially powerful word, when you want to blast a word beyond Merriam-Websters’ reach, enallage from the form classes. Brilliantificate nouns, verbs, adjectives, and adverbs. Don’t waste your time on structure words.
Unless, of course, you’re itching to say something like From me no froms. We are talking English here.
I can’t hope to answer all the questions you may be asking yourself right now, like What is an inflectional morpheme anyhow? or How do you diagram sentences? Mainly, I want to pull this one message out of the bottle: when it comes to parts of speech, you might not know what you think you know. As a writer in search of new life for old words, you just might decide to consider that discovery good news.
 Thomas P. Klammer, Muriel R. Schulz, and Angela Della Volpe, Analyzing English Grammar, 5th ed. (New York: Pearson Longman, 2007), 91. I’m grateful to this book’s coauthors, Drs. Klammer, Schulz, and Della Volpe, for their feedback on this post and on “You Don’t Know From Prepositions” (https://writing.rocks/prepositions-phrasal-verbs-verb-particles-adverbs-2/).
 Bryan A. Garner, Garner’s Modern American Usage, 3rd ed. (Oxford: Oxford University Press, 2009), 910.
 Klammer, Schulz, and Della Volpe, Analyzing English Grammar, 179.
 Muriel R. Schulz, e-mail to the author, June 2, 2012.
 Klammer, Schulz, and Della Volpe, Analyzing English Grammar, 85.
 Ibid., 12.
 Ibid., 91.
 Ibid., 86.
 Some pronouns, the troublemakers, prove the exception to this generalization. You didn’t expect English to lie down for this analysis, did you?
 Klammer, Schulz, and Della Volpe, Analyzing English Grammar, 95–96.
 For more on from and its fellows, including more reasons that we can’t automatically call from or any other word a preposition, see “You Don’t Know From Prepositions” (https://writing.rocks/prepositions-phrasal-verbs-verb-particles-adverbs-2/).
 Klammer, Schulz, and Della Volpe, Analyzing English Grammar, 89.
 Arthur Plotnik, Spunk & Bite: A Writer’s Guide to Bold, Contemporary Style (New York: Random House, 2007), 113.
 To find out about inflectional morphemes, the distinction between form classes and structure classes, and the intricacies of diagramming sentences, see Analyzing English Grammar. For insights into diagramming sentences, see also Kitty Burns Florey, “Taming Sentences,” June 18, 2012, New York Times online series Draft, or Florey’s book Sister Bernadette’s Barking Dog: The Quirky History and Lost Art of Diagramming Sentences (Orlando: Harcourt, 2006).