Construction with "sein" + infinitive?

Answer 1

Let's look at some examples. When you say sein + infinitiv, we're going to make sure to sneak a ZU in there, and it translates into a sense of need or possibility.

Das Zimmer ist aufzuräumen. - The room needs to be cleaned up.

Meine Kompetenz ist nicht zu unterschätzen. - My ability is not to be underestimated.

Dem Kind ist jederzeit zu gehorchen. - The child is to be obeyed at all times.

Die Krankheit ist zu heilen. - The sickness [can be] healed.

These sentences fall under three categories:

Notwendigkeit aka necessity (e.g. the room that needs to be cleaned and the child that must be obeyed);

Möglichkeit aka possibility (e.g. the sickness that can be healed), and

Was Man Nicht Darf, or what you're not allowed to do (e.g. the ability that is not to be underestimated).

To format this construction, let's make an equation.

Noun + auxiliary verb + [ADV] + zu + INF.