Learn Italian: A causa dell'obbligo, ha dovuto adeguarsi. - Because of the obligation, he had to adapt himself.

When a modal verb like dovere is used with a reflexive verb, the choice of the auxiliary depends on where the reflexive pronoun goes. Because the pronoun si is attached to the end of the infinitive to form adeguarsi, the modal verb keeps its default auxiliary, which is avere.

If I wanted to put the reflexive pronoun si before the conjugated verb, how would the phrase change?

If you move the pronoun to the front, the reflexive nature of the phrase forces the auxiliary to change from avere to essere. The phrase would become si è dovuto adeguare. Both structures are completely natural and mean the exact same thing.

Is adeguarsi always reflexive, or can I use just adeguare?

You can use the non-reflexive adeguare when you are adjusting or adapting an external object, such as adjusting prices or updating a plan. When someone adapts themselves to a situation, as in this sentence, it becomes the reflexive adeguarsi.

Why do we use a causa dell' instead of perché l'?