it may be answered:
It has already been explained that an explicit text governing every individual instance of the rulings is not obligatory; indeed, it is not even possible. The imamate is itself one such ruling. Explicitly designating every person who will hold any position of authority over the Muslims until the Hour comes (1) is impossible and has never occurred. Explicitly designating one particular person rather than another does not amount to designating every individual; it is merely an explicit designation (2) of some particular individuals.
At that point, if it is said:
“It is possible to designate an imam explicitly and to delegate to him (3) the authority to designate his successor explicitly.”
[It may be answered: It is likewise possible to designate explicitly whomever is appointed as successor] (4) by the imam, as well as whomever he takes as his minister; an explicit designation to that effect would more fully accomplish the intended objective.
Moreover, regarding the imam who is personally designated: is he (5) infallible with respect to those whom he appoints to office, or is he not infallible? If he is infallible, then all his deputies must necessarily be infallible. Yet all of this (6) is self-evidently false. If he is not, he may appoint (7) someone who is not infallible as his successor. Thus, the existence of an infallible imam would not secure the intended objective in every age.
If it is said:
“He is infallible with respect to the person whom he appoints to succeed him, but not with respect to anyone he deputizes during his lifetime.”