Stick to Basic Law, even if it means changing it
Not one word of the Basic Law has been changed since it was adopted by the National People's Congress almost 15 years ago. Beijing has always rejected any calls for amendments. There are good reasons for adopting this cautious approach.
But there may be rare circumstances in which altering the text is the best way to resolve a problem. Beijing's apparent desire for the chief executive to serve a two-year term is perhaps one such situation.
Most constitutions allow for amendments to be made, although usually only after strict procedural requirements have been met. The US constitution, for example, has been amended 27 times over the past 216 years. China's constitution has been altered on four occasions, including changes made last year.
No decision to amend the Basic Law should be taken lightly. It provides Hong Kong with many crucial guarantees that define the parameters of the 'one country, two systems' concept.
The post-handover arrangements would crumble if the constitution was subjected to frequent changes.
But this does not mean the Basic Law is cast in stone. Article 159 provides a mechanism for making amendments and it contains some important safeguards.
No changes can be made which contravene China's 'basic policies' on Hong Kong. These are to be found in the Sino-British Joint Declaration and cover the core principles of the 'one country, two systems' concept.
This means that most of the Basic Law's provisions - including those dealing with Hong Kong's high degree of autonomy and human rights - cannot be altered. But the basic policies make no mention of the term that a chief executive must serve.
It may be that this is one area in which an amendment is possible.
Such a step is not desirable, but it is better than distorting or ignoring the clear meaning of the Basic Law.
The Basic Law, as it now stands, stipulates that a chief executive can serve only a five-year term. That is what should happen when Mr Tung's successor is elected.
But there are strong indications that the central government wants the next chief executive to serve two years instead, effectively seeing out the remainder of Mr Tung's term. It appears this might be done by way of a formal interpretation by Beijing.
But this would do violence to the plain wording of the Basic Law and undermine the arrangements governing our city's relationship with the mainland. Hong Kong's rule of law will also be seriously damaged.
If Beijing insists on a two-year term, it will effectively be changing the Basic Law. The central government should therefore follow the procedure for an amendment. This would be constitutional and therefore not do so much damage to public confidence in the system.
An amendment would probably receive widespread support in Hong Kong, as even the democrats would prefer a two-year term - so long as it is in accordance with the law.
In practice, an amendment along these lines is probably not possible for the election of the next chief executive. It must be approved by the National People's Congress, which concludes its annual meeting on Monday. There is not enough time.
Technically, an NPC meeting can be called on other occasions. But this has never been done - even in times of emergency. It would not be right to take such a momentous step simply to cut short the term of the next chief executive.
The possibility of an amendment should have been seriously considered as soon as the issue arose - allowing time for this option to be exercised as a last resort.
Beijing is right to be concerned that any change to the Basic Law would cause international concern. But at least it would be constitutional. Imposing a two-year term by other means - in defiance of the Basic Law - would be far worse.