Learn Portuguese (Portugal): A degradação é grave e tenho medo de que o muro se desmorone. - The degradation is severe and I am afraid that the wall will collapse.

While English simply uses 'afraid that', Portuguese often retains the preposition that a word naturally requires before adding the conjunction que. The base expression is ter medo de (to be afraid of), so when a whole clause follows, we keep the preposition, creating ter medo de que.

Why is the verb desmoronar-se in the subjunctive mood (desmorone)?

Expressions of fear and emotion trigger the subjunctive mood in the subordinate clause that follows them. Because tenho medo de que shows emotional subjectivity, the verb describing the feared event must be in the present subjunctive, hence desmorone instead of the present indicative desmorona.

Why is the wall collapsing translated with the reflexive pronoun se in se desmorone?

The verb desmoronar-se (to collapse or crumble) is usually pronominal when a structure falls apart on its own. The se shows that the wall is undergoing the action of crumbling itself, rather than an outside force actively knocking it down.

Could we attach the pronoun to the end of the verb and write que o muro desmorone-se?