This study investigates why researchers have trouble determining when learners acquire inverted and statement forms of yes/no questions. Researchers have difficulty designing studies on this subject because this area of language is not fully rule-governed or systematic. The choice of the form may be based on two speakers' foreknowledge of each other, the context of the question utterance, and/or the question's relationship to prior utterances in the dialogue. The question form used is also governed by the degree of pre-supposition of a yes or no answer. The function of the question to elicit information, to change the topic, to indicate understanding or confirmation, to display interest, and to encourage, also contributes to determining whether an inverted question form or a statement form with rising intonation will be used. When questions formed by six Spanish-speaking free-learners of English were compared to those formed by native English speakers, it remained difficult to judge the appropriateness of the question form used because the experimenter could not know the degree of presupposition on the question-asker's part. With a non-native speaker, there is no variable which reflects whether he has internalized the interrelationship between the form and pre-supposition. Without this, language researchers cannot ascertain when the acquisition of inverted and statement question forms occurs in second language learners. (PMJ)