The same statement can be both true and false. The sum of the interior angles of a triangle is 180 degrees. Performatives are expressions which create social facts. Take at least one course in logic. When a sentence can express more than one statement, and we cannot determine which statement the author of the sentence intended to express, the sentence is ambiguous.
Ambiguity can be semantical, referential or syntactical.
Semantical ambiguity occurs when a word or phase has more than one meaning. Referential ambiguity occurs when a noun or pronoun could refer to two or more different individuals, and context does not allow us to determine which. Faulty reasoning due to semantical or referential ambiguity is equivocation. Syntactical ambiguity occurs when the structure of a sentence allows more than one interpretation of that sentence. Faulty reasoning due to syntactical ambiguity is called amphiboly.