Questions & Answers about Er hätte in den Rückspiegel schauen müssen.
Why does this sentence use müssen instead of sollen for 'should have'?
In German, expressing that someone 'should have' done something is very commonly translated using the past subjunctive of müssen (hätte ... müssen). This literally means 'he would have had to'. You could also use sollen (hätte schauen sollen), but müssen is stronger and emphasizes a necessary rule or safety requirement that was ignored.
Why are there two infinitives (schauen müssen) at the end instead of a past participle like gemusst?
This is due to a special German rule called the double infinitive. Whenever a modal verb like müssen is used in a perfect tense along with another action verb (schauen), the modal verb drops its past participle form (gemusst). Instead, both verbs take their dictionary infinitive forms and stack up at the very end of the sentence.
Why is in den Rückspiegel in the accusative case here?
The word in is a two-way preposition that takes the accusative case for direction and the dative case for a fixed location. Even though the driver isn't physically moving into the mirror, directing your gaze toward a target counts as a directional action in German grammar, which requires the accusative den.
Why does the sentence use hätte instead of hat?