I confess in this analysis to having been influenced long ago by Hans Kelsen and his theory of the grundnorm.  Kelsen said that to understand a legal system you have to find the basic norm or rule by which the making of laws is determined.  You do not need to know the source of that basic rule — that is, whether it was an act of God or of man.  All you need to know is that it works.  Normally, any law or any constitution adopted in accordance with that basic rule or grundnorm is legitimate, but only if the total legal system is effective.  If it ceases to be effective — that is, if it is no longer recognized or accepted by the people it is to govern — then mere formal legal legitimacy will not save it, and it is likely to be replaced by another system that is generally acceptable and therefore effective.  In other words, political legitimacy is essential; legal legitimacy is desirable but not necessary.  Or put another way, nothing succeeds like success.  The only really good constitution is a constitution that works.1  Unlike many legal philosophers, Hans Kelsen has been widely cited in the courts, particularly in countries of the Commonwealth where judges have had to cope with coups d’état, revolutions, and other legal discontinuities in government.  As you can imagine, he has been a great comfort to the judicial mind when faced with the need to recognize new governments which enjoy some political legitimacy but lack legal legitimacy.

Therefore, you can have a perfectly respectable constitution even though it is not legally legitimate.  Two examples will illustrate the point.  First, the British constitution and the monarchy.  At the risk of accusations of treason, I could argue that in point of law our true monarch is some obscure descendant of the Jacobite Stuarts.  If you go back to the Glorious Revolution of 1688, when James II left the country and the English put on the throne William and Mary of the House of Orange, it was not at all according to the rules.  If it had happened in 1980, all ten Canadian provinces would have taken references on the subject to their courts of appeal!  The fact is that a change in succession to the throne was authorized by a Parliament which was not summoned in accordance with the preexisting rules and whose decision was not given royal assent because there was no sovereign on the throne to give assent.  But it worked.  Starting with this illegitimate origin, the British Parliament has governed the succession to the Throne ever since.  Nothing succeeds like success, and who would today challenge the political legitimacy of the British Constitution? 2

Secondly, consider the American Constitution.  What constitution is more eminently respectable today, more hallowed by the people it governs?  But legally, it carries the bar sinister.  It is from the wrong side of the
1. See. e.g., Kelsen, General Theory of State and Law (1945) at 115-23.
2. See Maitland, Constitutional History of England (1908) 281-88; Taswell-Langmead, English Constitutional History (Plucknett, ed. 10th ed. 1949) 491-521.

  »  3-4