Buddhaghosa on the four categories of questions
Writing in the fifth century C.E., Buddhaghosa—the primary commentator of the Theravada tradition—explained the Buddha’s four categories of questions in terms of the formal or logical structure of the question.
“If asked, ‘Is the eye inconstant?’ one should answer categorically, ‘Yes, it’s inconstant.’ This pattern [holds] with regard to the ear, etc. This is the categorical question. If asked, ‘Does inconstant mean eye?’ one should answer analyzing, ‘Not just the eye; the ear is also inconstant, the nose is also inconstant.’ This is an analytical question. If asked, for example, ‘Is the eye like the ear? Is the ear like the eye?’ and one cross-questions, ‘In what sense are you asking?’ then if told, ‘I am asking in the sense of seeing,’ one should answer, ‘No.’ If told, ‘I am asking in the sense of inconstancy,’ one should answer, ‘Yes.’ This is a cross-questioning question. When asked, for example, ‘Is the soul the same thing as the body?’ one should put it aside, (saying,) ‘This is unanswered by the Blessed One.’ This question is not to be answered. This is a question to be put aside. Thus the form in which the question is presented is the measure of the four ways of answering questions. It is under the guidance of these [categories] that a question should be answered.” — Commentary to DN 33 [emphasis added]
From this perspective, a question deserving a categorical answer is one that, in formal terms, reads, “ Is all A, B?” (“Are all tigers striped animals?”) This type of question can be clearly answered Yes or No.
The next two categories of questions are those that could lead the answerer to being trapped in a logical fallacy, and so must be treated analytically or with a cross-question to avoid the trap. The question deserving an analytical answer is one that—after establishing that all A is B—asks, “Is all B, A?” (“Are all striped animals tigers?”) The trap here would be, “If all A is B, then all B is A” (e.g., “If all tigers are striped animals, then all striped animals are tigers;” “If the eye is inconstant, then all inconstant things are the eye”). Thus an analytical answer would show that inconstancy covers other things beside the eye as well: “All A is B, but not all B is A.”
The question deserving cross-questioning is one that has to be clarified before it can be answered. Thus the cross-question is simply, “What do you mean?” Buddhaghosa’s example is of a question that could lead to the trap, “If all A is B, and all C is B, then if all A is also D, all C is also D” (e.g., “If all tigers are striped animals and all zebras are striped animals, then if all tigers are cats, all zebras are cats;” “If the eye is inconstant and the ear is inconstant, then if the eye sees, the ear sees”). The cross-question is necessary to clarify the sense of the question and to make the point that even though the eye and ear are similar in some ways, that does not mean that they are similar in all ways: “All A is B and all C is B; all A is also D, but it is not the case that all C is also D.”
Unlike his handling of the second and third categories, Buddhaghosa illustrates the fourth category with an example from the Canon—one of the ten “undeclared issues” (avyākata-dhamma)—but this leads him to an inconsistency. Although he says that the form of the question is what determines the response-strategy it deserves, there is nothing about the formal structure of this question to indicate why it falls into a separate category. He simply notes that because the Buddha put it aside it should stay there.
However, in terms of the first three categories, it is obvious that Buddhaghosa—and the tradition he draws from—is thinking in terms of the questions and logical traps encountered in formal debate, especially of the sort that shaped the way the commentarial tradition evolved. Thus these categories are determined strictly by their logical form. The difficulty in accepting Buddhaghosa’s interpretation here is that the Buddha never engaged in formal debates of this sort, and there is no record in the Pali Canon of his ever encountering the types of question that Buddhaghosa uses to explain the second and third categories. Also, Buddhaghosa’s example of a cross-questioning question comes nowhere near to doing full justice to the many ways in which the Buddha used and encouraged cross-questioning in the discourses. Thus it is unlikely that Buddhaghosa’s examples—and the definitions determining their classification—correspond to what the Buddha had in mind when formulating his four response-strategies, and they certainly don’t reflect the use of these strategies in the Buddha’s hands.