The basic unit involved in mathematical reasoning is a mathematical statement. Let us start with two sentences:
In 2003, the president of India was a woman.
An elephant weighs more than a human being.
When we read these sentences, we immediately decide that the first sentence is false and the second is correct. There is no confusion regarding these. In mathematics such sentences are called statements.
A sentence is called a mathematically acceptable statement if it is either true or false but not both.