The reason for the retention of shall or should is that, in such cases, the second or third person of the indirect discourse represents the first person of the direct.

The change from shall (after says) to should (after said) is a mere change of tense, according to the rule in [§ 434].

Note. The general principle is, to retain in the indirect discourse the auxiliary of the direct, simply changing the tense if necessary ([§ 434]). This principle of course covers the use of you or he shall or should to represent I shall or should. There is, however, one important exception to the general principle: when its application would result in the use of I will or I would to express mere futurity, I shall or I should is employed. Thus, John says to Charles, “If you fall overboard, you will drown”

; but Charles, reporting this, must say, “John tells me that, if I fall overboard, I shall [NOT will] drown.” The general rule, then, may be stated as follows: The indirect discourse retains the auxiliary of the direct (with a change in tense, if necessary), unless such retention makes will or would express simple futurity in the first person,—in that case, shall or should is used.

439. The following sentences illustrate the correct use of shall and will, should and would, in the indirect discourse:—

IX. INDIRECT QUESTIONS