EG: Studying is good for you.
Gerunds are used after prepositions, but not usually after 'to'. The gerund looks identical to the present participle, which is used after the auxiliary verb 'to be', but are not the same as they do not function as main verbs. Gerunds are used after certain words and expressions, as is the infinitive, so it is useful to try to learn which form an adjective, etc., takes.
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