Senate Concurrence Not Required
Article 2 of the Vienna Convention on the Law of Treaties defines a treaty as “an international agreement concluded between states in written form and governed by international law, whether embodied in a single instrument or in two or more related instruments and whatever its particular designation.” International agreements may be in the form of (1) treaties that require legislative concurrence after executive ratification; or (2) executive agreements that are similar to treaties, except that they do not require legislative concurrence and are usually less formal and deal with a narrower range of subject matters than treaties.
Under international law, there is no difference between treaties and executive agreements in terms of their binding effects on the contracting states concerned, as long as the negotiating functionaries have remained within their powers. Neither, on the domestic sphere, can one be held valid if it violates the Constitution. Authorities are, however, agreed that one is distinct from another for accepted reasons apart from the concurrence-requirement aspect. As has been observed by US constitutional scholars, a treaty has greater “dignity” than an executive agreement, because its constitutional efficacy is beyond doubt, a treaty having behind it the authority of the President, the Senate, and the people; a ratified treaty, unlike an executive agreement, takes precedence over any prior statutory enactment.
Petitioner parlays the notion that the Agreement is of dubious validity, partaking as it does of the nature of a treaty; hence, it must be duly concurred in by the Senate. Petitioner takes a cue from Commissioner of Customs v. Eastern Sea Trading, in which the Court reproduced the following observations made by US legal scholars: “[I]nternational agreements involving political issues or changes of national policy and those involving international arrangements of a permanent character usually take the form of treaties [while] those embodying adjustments of detail carrying out well established national policies and traditions and those involving arrangements of a more or less temporary nature take the form of executive agreements.” 
Pressing its point, petitioner submits that the subject of the Agreement does not fall under any of the subject-categories that are enumerated in the Eastern Sea Trading case, and that may be covered by an executive agreement, such as commercial/consular relations, most-favored nation rights, patent rights, trademark and copyright protection, postal and navigation arrangements and settlement of claims.
In addition, petitioner foists the applicability to the instant case of Adolfo v. CFI of Zambales and Merchant, holding that an executive agreement through an exchange of notes cannot be used to amend a treaty.
We are not persuaded.
The categorization of subject matters that may be covered by international agreements mentioned in Eastern Sea Trading is not cast in stone. There are no hard and fast rules on the propriety of entering, on a given subject, into a treaty or an executive agreement as an instrument of international relations. The primary consideration in the choice of the form of agreement is the parties’ intent and desire to craft an international agreement in the form they so wish to further their respective interests. Verily, the matter of form takes a back seat when it comes to effectiveness and binding effect of the enforcement of a treaty or an executive agreement, as the parties in either international agreement each labor under the pacta sunt servanda principle.
As may be noted, almost half a century has elapsed since the Court rendered its decision in Eastern Sea Trading. Since then, the conduct of foreign affairs has become more complex and the domain of international law wider, as to include such subjects as human rights, the environment, and the sea. In fact, in the US alone, the executive agreements executed by its President from 1980 to 2000 covered subjects such as defense, trade, scientific cooperation, aviation, atomic energy, environmental cooperation, peace corps, arms limitation, and nuclear safety, among others. Surely, the enumeration in Eastern Sea Trading cannot circumscribe the option of each state on the matter of which the international agreement format would be convenient to serve its best interest. As Francis Sayre said in his work referred to earlier:
x x x It would be useless to undertake to discuss here the large variety of executive agreements as such concluded from time to time. Hundreds of executive agreements, other than those entered into under the trade-agreement act, have been negotiated with foreign governments. x x x They cover such subjects as the inspection of vessels, navigation dues, income tax on shipping profits, the admission of civil air craft, custom matters and commercial relations generally, international claims, postal matters, the registration of trademarks and copyrights, etc. x x x
And lest it be overlooked, one type of executive agreement is a treaty-authorized or a treaty-implementing executive agreement, which necessarily would cover the same matters subject of the underlying treaty.
But over and above the foregoing considerations is the fact that––save for the situation and matters contemplated in Sec. 25, Art. XVIII of the Constitution––when a treaty is required, the Constitution does not classify any subject, like that involving political issues, to be in the form of, and ratified as, a treaty. What the Constitution merely prescribes is that treaties need the concurrence of the Senate by a vote defined therein to complete the ratification process.
Petitioner’s reliance on Adolfo is misplaced, said case being inapplicable owing to different factual milieus. There, the Court held that an executive agreement cannot be used to amend a duly ratified and existing treaty, i.e., the Bases Treaty. Indeed, an executive agreement that does not require the concurrence of the Senate for its ratification may not be used to amend a treaty that, under the Constitution, is the product of the ratifying acts of the Executive and the Senate. The presence of a treaty, purportedly being subject to amendment by an executive agreement, does not obtain under the premises.
Considering the above discussion, the Court need not belabor at length the third main issue raised, referring to the validity and effectivity of the Agreement without the concurrence by at least two-thirds of all the members of the Senate. The Court has, in Eastern Sea Trading, as reiterated in Bayan, given recognition to the obligatory effect of executive agreements without the concurrence of the Senate:
x x x [T]he right of the Executive to enter into binding agreements without the necessity of subsequent Congressional approval has been confirmed by long usage. From the earliest days of our history, we have entered executive agreements covering such subjects as commercial and consular relations, most favored-nation rights, patent rights, trademark and copyright protection, postal and navigation arrangements and the settlement of claims. The validity of these has never been seriously questioned by our courts.