I have a question regarding following quote:
Was die Alarmglocken eines jeden Steuerexperten hätte aufschrillen lassen müssen,
ließ die Fachleute der Deutschen Bank offenbar kalt.
Why are there like 3 infinitives stacked together? And why is there hätte without partizip 2 following it? I could've understood if it were aufschrillen lassen gemusst. Can you refer to some grammatical article explaining this?
The sentence can be derived like this, by adding one verb at a time:
Die Alarmglocken schrillen auf.
Das läßt die Alarmglocken aufschrillen. (lassen + Infinitiv; "kausativ")
Das muß die Alarmglocken aufschrillen lassen. (müssen + Infinitiv)
Das hätte die Alarmglocken aufschrillen lassen müssen. (haben + Ersatzinfinitiv)
In the perfect, modal verbs use the Ersatzinfinitiv instead of the Partizip 2 (as long as they are combined with another infinitive, such as lassen in this case).
Since your sentence is verb-final and there are two or more non-finite verbs in the end, you also get an unexpected position for hätte: it occurs in front of the other verbs and not in last position. The position has been called Oberfeld.
was die Alarmglocken hätte aufschrillen lassen müssen
