Gerunds and infinitives can function as nouns or verb forms in sentences. Gerunds are formed with -ing and can be subjects, objects or subject complements. They take singular verbs as subjects. Only gerunds can be objects of prepositions. Infinitives are formed with to plus the base verb form and can be subjects or objects. Certain verbs select either gerund or infinitive complements. Both gerunds and infinitives can occur in various tense and aspect forms like perfect, progressive, passive.