in aid of legislation is "mandatory", the "question hour" is not

The framers of the 1987 Constitution removed the mandatory nature of such appearance during the question hour in the present Constitution so as to conform more fully to a system of separation of powers.⁸⁸ To that extent, the question hour, as it is presently understood in this jurisdiction, departs from the question period of the parliamentary system. That department heads may not be required to appear in a question hour does not, however, mean that the legislature is rendered powerless to elicit information from them in all circumstances. In fact, in light of the absence of a mandatory question period, the need to enforce Congress’ right to executive information in the performance of its legislative function becomes more imperative. As Schwartz observes:

Indeed, if the separation of powers has anything to tell us on the subject under discussion, it is that the Congress has the right to obtain information from any source – even from officials of departments and agencies in the executive branch. In the United States there is, unlike the situation which prevails in a parliamentary system such as that in Britain, a clear separation between the legislative and executive branches. It is this very separation that makes the congressional right to obtain information from the executive so essential, if the functions of the Congress as the elected representatives of the people are adequately to be carried out. The absence of close rapport between the legislative and executive branches in this country, comparable to those which exist under a parliamentary system, and the nonexistence in the Congress of an institution such as the British question period have perforce made reliance by the Congress upon its right to obtain information from the executive essential, if it is intelligently to perform its legislative tasks. Unless the Congress possesses the right to obtain executive information, its power of oversight of administration in a system such as ours becomes a power devoid of most of its practical content, since it depends for its effectiveness solely upon information parceled out ex gratia by the executive.⁸⁹ (Emphasis and underscoring supplied)

Sections 21 and 22, therefore, while closely related and complementary to each other, should not be considered as pertaining to the same power of Congress. One specifically relates to the power to conduct inquiries in aid of legislation, the aim of which is to elicit information that may be used for legislation, while the other pertains to the power to conduct a question hour, the objective of which is to obtain information in pursuit of Congress’ oversight function.

When Congress merely seeks to be informed on how department heads are implementing the statutes which it has issued, its right to such information is not as imperative as that of the President to whom, as Chief Executive, such department heads must give a report of their performance as a matter of duty. In such instances, Section 22, in keeping with the separation of powers, states that Congress may only request their appearance. Nonetheless, when the inquiry in which Congress requires their appearance is "in aid of legislation" under Section 21, the appearance is mandatory for the same reasons stated in Arnault.⁹⁰