Begging the Question

This is also called Petitio principii.

The often-abused expression begging the question has a specific meaning in logic, which is this: It is the fallacy in which the conclusion in assumed to be true inside the premise.

Example

I think therefore I am. - René Descartes. Here there is an unstated conclusion in the premise, because one cannot think unless one is.

I can see you therefore I am not blind.

Weaknesses

It confuses the conclusion and the premise, or they are the same.