The document discusses gerunds and infinitives. A gerund is a verb form ending in "-ing" that functions as a noun. An infinitive is the base form of a verb preceded by "to" or without "to". Gerunds can function as subjects, objects of prepositions, or in compound nouns. Infinitives are used after modal verbs or as subjects/objects. Certain verbs select gerunds or infinitives depending on subtle differences in meaning.