To make a conclusion whether Helen Keller would or would not have learned without Anne Sullivan would be an appeal to ignorance fallacy.
Explanation:
There is no doubt about Anne Sullivan’s role in Helen Keller’s learning, but saying she would not have learned had Sullivan not come to teach her would be a hasty conclusion. There was every chance that if not Sullivan, someone else, may be after a year or more, had come to teach Helen Keller. And who knows she might have learned even more and faster without Sullivan. Reaching this or its opposite conclusion would be a fallacy of appeal to ignorance.
Appeal to ignorance is a fallacy by which we consider a proposition to be true because it has not been proved false, or a proposition to be false because it has not been proved true.
