The definition of mathematical truth is confusing.
Let P and Q denote the statements 'I'm a man' and '$1<x<2$', respectively.
P is truly (naturally) true because it is really true.
In natural language, we cannot determine whether Q is true or false. However in math, as far as I understand, Q has a truth set that is not empty; therefore it is mathematically true.
That there are two ways to determine whether something is true or false confuses me.