Four hypotheses concerning the linguistic structure of yes-no questions and their answers are considered as hypotheses relating to the abstract structure of yes-no questions and to this abstract structure in all human languages. The universal base hypotheses are the following: (1) The abstract representation of all yes-no questions includes two disjunctively connected declarative sentences, symbolizable as X or Not-X. (2) The abstract representation includes a component paraphrasable as I ASK YOU TO TELL ME. (3) For a semantic subclass of yes-no questions, those called "biased" ones, the abstract representation includes an additional declarative sentence. (4) Answers and questions are in a member-to-class relationship with each other. Eighty-five languages form the data base against which these hypotheses are tested. The structure of all yes-no questions is shown to be, on some level of representation, complex rather than simple. The underlying X or Not-X structure is shown to be subordinated to a sentence paraphrasable as I ASK YOU TO TELL ME. The underlying structure of tag questions differs from that of neutral yes-no questions since it contains an additional copy of the suggested answer. Evidence is also found to support the fourth hypothesis. (Author/PM)