Strong 2D -- A Canape Solution

If you open 2D to show any strong hand with 4+ diamonds, 2C instead tending to deny 4+ spades, then the approach resembles a tendency canape approach.

Consider opening 1S. If you open 1S with 5+ spades (five-card majors), you still might open another suit if holding five spades but six of the other suit. This is rare, but it can still happen and does happen.

If you play four-card majors, you do not open 1S any time that you have four spades. Rather, you will still tend to bid long suits first. However, some 4-card openings happen because of the structure of rebids.

With pure canape, however, a person will open any time they have four spades unless they have a second suit and spades are LONGER, in which case they keep the spades in reserve for the second round, as a canape sequence is one where the longer of two suits is bid second.

with "tendency" canape, however, you might open the long suit first or might open the shorter of two suits first, depending on some factor, such as perhaps range.

With a strong 2D opening used any time the person has four spades, the principle is very much tendency canape. Consider the rebids I use, after a "normal" 2H relay:

2S shows 5+ spades. This is a normal sequence, similar to 2C-P-2D-P-2S in standard. hence, this is NOT canape. However...

3C, 3D, and 3H each are CANAPE bids. Longer in the second suit. Whereas the "canape" aspect could be called "implicit" in the sense that 2D is an artificial opening that "just happens" to show 4+ spades, in reality this is an identical sequence to a theoretical alternative of a spade opening and a jump rebid to this level if the jump rebid was canape.

Similarly, my strong 2C idea has its own implicit canape, as to hearts, but on the second round. The opening is truly artificial, as it carries merely a tendency limitation (not 4+ spades unless 24+ and balanced). No suit is SHOWN; instead, the LIKELIHOOD of a suit (spades) is indicated negatively.

However, the heart rebids fall in two camps -- 2H (sequences for 5+ heart hands) and 2S (canape or 4-4-4-1 hands). Maybe, a double-delay tendency canape approach.

Thus, it seems to me that the two-way structure that best solves the strong-hand problem is structured most effectively with a tendency canape philosophy.