Counterfactual fallacy

I taught you logic. So, if I hadn't taught you logic, you never would have learned logic at all. A counterfactual fallacy occurs when someone states a fact, states that something would be true if the stated fact were not true, and provides no evidence for this position.

The fallacy is a causation fallacy and an informal fallacy.

Alternative names

 * argumentum ad speculum
 * hypothesis contrary to fact
 * "what if"
 * wouldchuck

Form
Or even more egregiously:

The second form doesn't even explain the causal connection between A and B; it really is just wild speculation. The first form is a special case of denying the antecedent, applied to counterfactual reasoning; it ignores the possibility of B still occurring as an effect of causes other than A, even if A had not occurred.

Speculative evidence
You commit this fallacy if you draw conclusions from evidence that hasn't been collected yet, but that, one supposes, would have come out in favor of one's own opinion.

If there is no evidence to support a particular point, do not rely on that point to carry your argument. If pressed on a point where there is not valid evidence to support it, acknowledge the lack of data and suggest that the matter needs to be investigated in order to resolve the disputed issue.

Explanation
Confusing "what might have been" with "what ought to have been"; speculating what would have happened in other circumstances, then drawing conclusions from the speculation.

Examples

 * "We'd never have all this crime if [X] was president." This is unknowable because [X] isn't president.
 * "In this country citizens are permitted to own guns. If guns were outlawed, citizens would be unable to protect themselves and there would be an uncontrollable crime wave."