Superpins – What if pinned pieces don’t check?

According to chess laws, a piece that’s absolutely pinned to its king still retains its power to check the opponent’s king. There are good reasons for this rule, and yet in the end it’s only a matter of convention. There is in fact nothing inherently wrong or logically inconsistent with the converse notion, that a pinned unit loses its checking power. Suppose we apply such an unorthodox rule to chess – what are the consequences? In problem compositions, the realm of fairy chess deals with all kinds of rule modifications, and this particular condition is known as Superpins. It turns out that Superpins – seemingly a minor rule change – is quite profound in bringing about many curious and non-intuitive effects. Let’s consider a position that demonstrates some of the special tactics possible under this condition, before looking at two problems that showcase such ideas in striking ways.

With Superpins operating in this position, both the white queen and knight are pinned and so neither is checking the black king. If it’s Black’s turn, moves like 1…Ke6 and 1…Kxf6 are legal as the potential white attacker in each case remains pinned. Black moves that unpin such an attacker are illegal, because that would trigger a white check, e.g. 1…Rg7?? would unleash the queen (“??” denotes an illegal move in this blog). The black queen is severely restricted for this reason; it only has three legal moves to a8, c6, and d5. Unpinning the white queen by interposition with 1…Sf4?? is similarly forbidden. It is possible to parry a check by pinning the checking piece, e.g. 1…Se5+ 2.Re4.

If it’s White’s turn, the queen has an unexpected legal move off the pin-line: 1.Qg7, which by pinning the black rook nullifies its check. More obviously, White can execute a special type of check by unpinning a white unit that’s already observing the king, through capturing the black pinner or interposing on the pin-line, e.g. 1.Rf4+ results in a queen check, or 1.Re4+ gives a double-check with the rook and knight. Another sort of unpinning check can be made by the king itself, e.g. 1.Ke3+ delivers a double-check by the queen and knight.

An intricate Superpins effect is the pin/unpin chain, which comes about as a natural consequence of the unorthodox rule. Given that a pinned piece has no checking power, and that checking power is required to pin, it follows that a pinned piece has no pinning power either. Therefore if piece X is pinning piece Y, and then X itself gets pinned by a third piece, X will suddenly lose its pinning power and Y will regain its moving and checking abilities. In the diagram, the black queen (X) is pinning the white knight (Y); if White pins the queen with 1.Ra7, the black piece no longer has the power to check and thus the knight is freed to move and impose a real check on the black king. Another pin/unpin chain is exemplified by 1…Se5+ 2.Re4+ Qxd5+, when the pinning queen deactivates the white rook so that the knight is unpinned and gives an immediate check.

Despite how Superpins neatly brings about a wealth of intriguing effects with a simple rule change, it’s a neglected area in fairy chess composition. The British IM-composer Colin Sydenham is almost alone in exploring the condition and he has produced several first-rate examples. His diagram above serves as a fine introduction that renders some of the basic tactics achievable. If this were an orthodox mate-in-2 problem, any white king move would solve since the threat of 2.Sg6 cannot be met except by 1…e3, which permits 2.Qd4. Under Superpins, only one king move succeeds because the black rook can utilise the special rule to defeat the alternatives. You might want to have a go at solving this before reading further!

Five try-moves by the king are refuted by the rook in different ways. (1) 1.Kh7? leaves g5 guarded solely by the h4-pawn and places the king on the same file as that pawn. After 1…Rh1! pinning the pawn, 2.Sg6+ isn’t mate because of 2…Kg5! (2) 1.Kh6? Rd1! and the check 2.Sg6+ is answerable by the pin 2…Rd6! (3) 1.Kh5? Rb5! sets up a half-pin on the fifth rank, such that 2.Sg6+ self-pins the f5-knight and legalises 2…Ke3/Kg3! (4) 1.Kg7? Rg1! Here the pin of the g4-pawn is unimportant as 2.Sg6+ would unpin it to regain control of f5. Rather, Black’s aim is to pin the checking knight with 2…Rxg4! (5) 1.Kf7? Rf1! and the f5-knight is liable to be pinned again, this time on a file opened by the black king itself: 2.Sg6+ Ke3/Kg3! Finally, the key 1.Kf6! compensates for the prospective pin on the f-file by guarding e5, so that the queen is relieved to counter 1…Rf1 with 2.Qxf1.

The second problem is much more complex and involves some hard-to-grasp variations. In the initial position, neither the g4-pawn nor the e4-rook is giving check as each unit is pinned. The latter pin actually restricts the white queen as well, since a move like 1.Qd7?? would be an illegal self-check by activating the black rook. White’s knight on c4 is almost stuck due to a pin/unpin chain, e.g. 1.Sa3?? is forbidden because it would allow the black queen to pin the white one, which then no longer pins the checking rook. The knight does have a legal move that blocks the check of the activated rook, 1.Se3!, and it’s the key. The extended chain starting from the black queen means that the knight on e3 is really pinned and doesn’t check, but White threatens 2.Rxb5, which would release the white queen to re-pin the rook and thus mate with the knight.

Now six variations arise from various black defences against the threat, and we will first consider the four that are not so difficult. In these lines, Black defends in standard ways, such as by targeting the e3-knight, but these moves inadvertently free the white king, which then unpins two units simultaneously to give a double-check mate. 1…Bf2 2.Kxf2, 1…Sf1 2.Kxf1 (1…Sc4?? is illegal), and 1…Qxd3+ 2.Kxd3 – these all employ the e3-knight and g4-pawn for the deadly double-attack. 1…Rxe3+ is legal since the white queen is pinned, but 2.Kxe3 mates by unpinning that piece as well as the g4-pawn.

The last two variations utilise pin/unpin chains intensively. 1…Rxe5 creates a flight-square on f4 (2.Rxb5+? Kxf4), and it’s answered by the remarkable 2.Rc4. This move intercepts the pin-line of the black queen to give a single check by the white queen – single because the e3-knight remains pinned by the rook – but why is it mate? It turns out that all attempts by Black to handle this queen check are illegal as they would activate the e3-knight and leave Black still in check: (1) 2…Se4?? unpins the white knight directly, (2) 2…Re4?? self-pins the rook to the white queen and thus activates the knight, and (3) 2…Qxc4?? (aiming to re-pin the white queen) self-pins the black rook again, this time to the a5-rook.

With 1…Qc4, the queen steps away from the menacing a5-rook while maintaining the chain that stops the e3-knight from checking. Now 2.Rxc4+? does check with the knight but it lets the black king escape to g6. The correct response is 2.Bxc7, a single check by the a5-rook. This is another subtle mate that relies on the same tactic just seen, that Black cannot legally interpose on the mating line because that would activate the e3-knight. Hence (1) 2…Re5?? self-pins the rook to the a5-rook, (2) 2…Qc5/Qd5?? directly unpins the white queen, which thereby pins the rook, and (3) 2…Qb5?? creates the most elaborate pin/unpin chain of this problem: by pinning itself to the a5-rook, the black queen releases the white one, which then pins the rook, causing it to free the checking knight. Thus four pin-lines operate simultaneously to ensure that 2.Bxc7 mate cannot be foiled. A marvellous composition!