A good answer: http://blog.darkbuzz.com/2014/03/counterfactuals-math.html http://blog.darkbuzz.com/2014/03/counterfactuals-math.html "Mathematician Terry Tao e

A good answer: http://blog.darkbuzz.com/2014/03/counterfactuals-math.html http://blog.darkbuzz.com/2014/03/counterfactuals-math.html "Mathematician Terry Tao explains his version of counterfactual reasoning in three posts on The “no self-defeating object” argument. As he explains, many elementary theorems are very confusing to students because they are based on constructing some impossible object. There can be no impossible object, so the proof seems like a paradox. The contradiction is avoided by precise mathematical definitions and analysis."