Haber de + infinitive to express formal obligation or future action (perífrasis verbal)
Although it is more common to find it in literature and in formal content, in Spanish we can use the auxiliary verb haber + de + infinitive. This verbal structure is used in two different ways:
Haber de + infinitive: obligation, convenience, necessity
It expresses an obligation although not a strong one, or the convenience or necessity of doing something.
Have a look and listen to these examples:
Its more colloquial and informal equivalent is:
tener que/ deber/necesitar + infinitive
Tengo que/Debo/Necesito coger el tren de las diez para llegar a tiempo a mi destino.
Haber de + infinitive: future action.
Have a look and listen to these examples:
Its more colloquial and informal equivalent is:
the main verb in the future tense
Esta guerra acabará con la esperanza de paz de la gente.
¿Por qué habría de + infinitive? Why should/would...?
There is a slightly different connotation when we use "habría de" (i.e. haber in the conditional tense) in a question using ¿Por qué...? 
This is generally used indicating "why should/would something have a certain effect", normally within a conversation where there is an element of doubt about something. 
For example:
Remember:
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