When can the infinitive of a verb be used as a predicate?

Infinitives can be used as predicates, and gerunds can also be used as predicates. There are similarities and differences between the two when used as predicates.

1. An infinitive and a gerund are used as a predicate, which is equivalent to a noun used as a predicate. The meaning is to answer the subject "what". Such as:

1. Our plan is to keep the affair secret.

Our plan is to keep the affair secret. (The subject and predicate are equal)

2. Their job is making wheelchairs for disabled people.

Their job is making wheelchairs for disabled people. (Subject and predicate are equal)

2. Although infinitives and gerunds are used as predicates to answer the subject "what", there are still some differences between the two. Infinitives as predicates emphasize one-time, specific, and upcoming actions; gerunds as predicates emphasize general, abstract, and frequent actions. Such as:

1. His job is to paint the walls.

His job is to paint the walls. (One-time, specific, current thing to do, not his daily job)

2. His job is painting walls.

His job is painting walls. (This is his daily job)