The passive periphrastic is a Latin construct to express a sense of necessity in an action. It's called passive because it is expressed in a passive tense, so it's usually better to change it back to its active form when translating.

How are passive Periphrastics formed?

Strictly speaking, though, the passive periphrastic refers to the gerundive (a passive verbal adjective) plus sum. ... If the verb is transitive, the nominative gerundive (a predicate adjective agreeing with the subject in number and gender) is used with a tense of esse: 1. Vir videndus est.

Which participle is used in the passive periphrastic?

The future passive participle, also known as the gerundive, is used in the passive periphrastic in order to express obligation or necessity (often with a dative of agent), and also in gerundive phrases.