Why do scholars use the term "conditions and impediments of takfir" even though conditions are the opposite of impediments, and they could suffice with mentioning only one of them?

The condition (الشرط): That whose absence necessitates the absence of the ruling. It is an existent attribute whose non-existence necessitates the non-existence of the conditioned, such as ihsan (being a free, adult, married Muslim) for the obligation of stoning the fornicator.

The impediment (المانع): That whose existence necessitates the absence of the ruling. It is the opposite of the condition, so its existence necessitates the non-existence of the ruling, such as debt with the obligation of zakat.

The difference between them lies in the fact that the condition must be an existent attribute, whereas the non-existence of the impediment is a non-existent attribute. The effect of this is apparent in that, for the non-existence of the impediment, the default (original state) is sufficient, while for the condition, its realization is indispensable.