Perhaps the most important rule of chess is the very first one we learn and then forget about.  The article 1.1 of FIDE Laws of Chess states “The game of chess is played between two opponents who move their pieces alternately”. The key here is the word “alternatively”, without which chess would lose all its essence. The most sophisticated consequence of this rule is a player can never pass a move. This obligation to make a move gave birth to the concept called “Zugzwang”, a situation where any possible move will fatally weaken the position. Most novice chess players have heard of the term, but they tend to think that it’s a mysterious and advanced concept only known to the experts. The truth is almost every player, either knowingly or unknowingly, has used zugzwang in their games. Let’s consider a simple “king and rook versus king” endgame and grant the weaker side the option of passing. [caption id="attachment_134810" align="alignnone" width="300"] White to play - Can white win if black can pass his move? [/caption] Clearly it’s impossible for white to win this if black plays (or passes) correctly. The same goes for lots of other basic endgames as well. Funnily enough, this concept was known even before chess was chess!   The earliest Zugzwang The following position is from a  study composed by Shatranj masters in the 9th century. Shatranj was an old Persian board game considered the forerunner of modern chess. [caption id="attachment_134811" align="alignnone" width="300"] White to play and win[/caption] The white rook is dominating the black knight which is fatally stranded on an edge of the board. The rook must stand guard, so the white king must lend some help. The hasty 1.Kf4 runs into 1...Kd4, and it is white who must weaken his position. Instead white starts with 1.Kf5 Kd4 2.Kf4 and we got ourselves the earliest known Zugzwang/squeeze. After 2...Kc4 3.Kg3! Kd4, white wins with 4.Re1. A knight on the rim is grim [caption id="attachment_134846" align="alignnone" width="301"] A stamp celebrating Capablanca’s 100th birth anniversary (Photo - Colin Rose, “Chess on stamps”)[/caption] The former World Champion Jose Raul Capablanca is known for his exceptional endgames technique. The Cuban genius thrived on the simplicity and the clarity offered by an almost empty board. One such outstanding example (which did not even occur in a tournament game) was deemed famous enough to be granted its own postage stamp more than 70 years later. The position depicted in the stamp White to playThe mysterious thing about this position is that even though the stamp says “Capablanca - Lasker”,  it cannot be found in any database. According to the book “The Unknown Capablanca”, it never occurred over the board. Apparently Capablanca and Lasker played a short blitz match in 1914 and this position is a variation discussed during the post mortem of an endgame Capa won as white. We arrive at the critical position after 1.Nxc7 Nxc7. [caption id="attachment_134848" align="alignnone" width="300"] White to play[/caption] All of a sudden it seems like black is escaping with a draw. 2.Kxc7 leads to a stalemate and it’s not clear how white can prevent 2...Nxb5. Capablanca’s solution is quite stunning. 2. Ra8+!!, an incredible move.  Now black must play 2...Nxa8 (2...Kxa8 3.Kxc7 Ka7 4.Kc6) and white responds with 3.Kc8! And we have the most famous example in history of a claustrophobic knight. The position represents a neat Zugzwang. Black is forced to play 3...Nc7 4.Kxc7 and white wins. Interestingly, this supposedly postage stamp-worthy concept was anticipated by a relatively unknown player as early as 1898. [caption id="attachment_134849" align="alignnone" width="300"] Rose - Johnston (1898) - Black to play[/caption] Black won the game after 1...Qc1+ 2.Bg1 Qe1 3.Kg2 Qg3+ 4.Kh1 Qf2!! 5.Bxf2 Kxf2. A delightful combination worthy of rivalling Capablanca’s gem.