Unwarranted Assumptions

Fallacy
Let $p$ be a proposition whose truth value is to be proved (either true or false).

During the course of a logical argument it is permitted to make an assumption by use of the Rule of Assumption.

However, each of the assumptions being made has to be discharged before the proof of $p$ can be considered complete.

To fail to discharge all the assumptions is to commit the fallacy of unwarranted assumptions.

Also see

 * Begging the Question