Any verb in a sentence that does not function as a finite verb has to function as one of the three verbals:
Gerunds always function as nouns.
Object of Preposition: Mary was thinking (about playing golf.)
Predicate Noun: The best hobby is reading.
Direct Object: They love skiing.
An Example of Gerunds That Function as Objects of Prepositions
Gerundives "always" function as adjectives.
The book was on the table, closed and covered with dust. ["Closed" and "covered" modify "book."
Most textbooks refer to gerundives as "participles," but to do so is confusing. "Participle" designates the form of the word -- the "-ing," "-ed," "-en," etc. ending. Both gerunds and gerundives have participial form. Infinitives do not.
Adjective: This is a good place to rest.
Adverb: They came to play.
The similarity of verbals to finite verbs is often overlooked in pedagogical grammars. Verbals are condensed, or reduced versions of the basic sentence pattern. Like finite verbs, they have subjects and complements. We'll look at the subjects later, but first consider the easily understood complements.
Complements of Verbals
Logically, complements of verbals would seem to need little discussion, but I have found that people well-trained in traditional grammar are often surprised to realize that verbals can have complements just as finite verbs have and that these complements can be found and distinguished in the same way that one finds and distinguishes the complements of finite verbs, i.e., by making a question with "what or whom" after the verbal. Their surprise is another indication of the categorizing, rather than conceptualizing approach usually taken toward traditional syntax. Instead of looking for similarities, traditional grammarians have stressed differences. Note that the conceptual approach not only simplifies, it also suggests the relative importance of concepts: the subject/verb/optional complement pattern is basic not only to every main and subordinate clause, but also to every verbal. It is truly the fundamental pattern of the language!
Tenses of Verbals
Helping verbs are used to create tenses for verbal phrases. For now, you need not remember the names of the tenses. Just remember that a verbal can consist of more than one word. (In other words, it can be a verbal phrase.)