* Gerunds are verb forms ending in "-ing" that function exclusively as nouns. They can be the subject of a sentence, the object of a verb, or the object of a preposition.
* Progressive verbs (e.g., "is running," "was walking") describe an ongoing action. They are verb phrases, not independent nouns.
* Participles (e.g., "broken," "running," "written") can act as adjectives or parts of verb phrases. They can sometimes be used as nouns (e.g., "the running," "the fallen"), but they have other functions as well.
* Infinitives (e.g., "to run," "to eat") can function as nouns, adjectives, or adverbs. While they can be subjects or objects, they have broader grammatical roles.
Example:
* Gerund: _Running_ is good exercise. (Subject of the sentence)
* Participle: The _broken_ window needs repair. (Adjective)
* Infinitive: I want _to eat_. (Object of the verb "want")