Usually, we easily identify a word’s part of speech, but a given word’s grammatical category can shift, or one form of the word can differ in meaning from another, in a process called functional variation.
For example, note the change in meaning of fly in the following sentences: “He caught a fly” (noun), “He caught a fly ball” (adjective), “He will fly there tonight” (verb), and “He caught the ball on the fly” (part of an adverbial phrase). These and other types of functional variation are described below:
1. Nouns as Adjectives
Nouns are frequently employed to modify other nouns (for example, in “light fixture,” “grape jam,” and “railroad track”). However, problems include ambiguous usage, such as in the phrase “box set,” which can mean “a set in a box” (and is therefore better rendered “boxed set”) or “a set of boxes,” and adjective stacking, or employing an excessive series of nouns as adjectives.
2. Adjectives as Nouns
The reverse can take place, as when a phrase such as “a hypothetical situation” is truncated to the adjective turned noun hypothetical or when a person or a group is identified, for example, as in “the homeless.”
3. Nouns as Verbs
This type of transformation is ubiquitous in the business world and in other jargon-friendly environments, where terms for things such as impact, mainstream, and text become action words.
4. Verbs as Nouns
Present participles such as laughing are employed as nouns: In “Who was laughing?” laughing is a verb; however, it’s a noun in “Did you hear that laughing?” (although it would be better to use the noun laughter).
5. Verbs as Adjectives
Participles also serve as adjectives. To use the previous example, laughing can also modify a noun, as in “See that laughing girl?” (although one could also write, “See that girl laughing?”).
6. Adjectives as Verbs
Such shifts are so rare that the only ones that occur to me are terms I occasionally use in these posts: lowercase and uppercase, as in “Lowercase job titles after a name,” in which lowercase refers to an action involving job titles, rather than describing a type of treatment of a job title.
7. Prepositions as Adverbs
When one refers, for example, to “calling up reserves” or “casting off from the dock,” one is using idiomatic phrasal verbs to describe how calling or casting occurs, though some phrasal verbs are merely figurative; “calling up,” for example, involves no upward movement, while “casting off” literally results in one no longer being on the dock.
8. Conjunctions as Prepositions
In rare cases, a conjunction can serve as a preposition, as when but, which usually functions as a conjunction, as in “I was there, but I didn’t see you,” is employed as a synonym for except, as in “Everyone but you has agreed.”
9. Various Parts of Speech as Interjections
Most parts of speech can serve as an interruptive or exclamatory term, including nouns (“Dude!”), pronouns (“Me!), verbs (“See?”), adjectives (“Wonderful!”), and adverbs (“Slowly!”).