In a private box at the Italian Opera in Paris, in the autumn of 1858, a twenty-one-year-old from New Orleans sat down to a game of chess against two noblemen at once. The Duke of Brunswick and Count Isouard consulted over every move. Paul Morphy beat them in seventeen. It is one of the most reprinted short games in chess, and it has been used to teach one idea for more than a century and a half: bring your pieces into play before you attack.

That sentence sounds like advice you could put on a fridge magnet. The game is worth an evening because it shows you what the advice actually costs and what it buys.

The game in four movements

The early claim. On his third move, Black pins White's knight to the queen. It looks aggressive. But Black has no other piece developed to support the pin, and one move later he has to give up the pinning bishop to avoid worse. A claim you cannot back up is just a bishop in the wrong place.

The refusal. On move nine, Morphy could win a pawn. He doesn't. Taking it would let Black offer a trade of queens, and with the queens gone, White's lead in development would evaporate. Instead Morphy pins Black's other knight and keeps the pressure on. Most of us, in chess and out of it, take the pawn.

The spending. Then Morphy starts giving material away. A knight, to open a diagonal. A rook, to keep a pin alive. Finally his queen, to pull the one defender off the one square that matters. By the end he has a rook and a bishop left, and they give mate.

The count. Look at the final position and count what Black never used. The bishop on f8 and the rook on h8 have not moved all game. They are still there when the king falls, a few squares away, fully intact. Black had the material. It was not in play.

Who was playing

Paul Morphy was born in New Orleans in 1837 and learned the game as a boy. In 1858 he travelled to Europe and beat the strongest players he could find, which is why he was in Paris that autumn and why a duke wanted to play him. Within a couple of years he had stopped playing serious chess almost entirely, and he never really returned to it. He is often called the best player of his day. The title of world champion did not formally exist yet, so that is a judgement rather than a record.

His opponents were not professionals. Karl, Duke of Brunswick, was a wealthy enthusiast living in Paris, and Count Isouard was his companion at the board. They were strong enough to enjoy a game against Morphy and nowhere near strong enough to survive one. It matters that the game is a lesson rather than a contest. It shows a principle with unusual clarity because the defence was weak.

Why it is still taught

There are longer and deeper Morphy games. This one survives in teaching because it is short enough to remember, every move has a reason you can say out loud, and the ending is a picture: one rook and one bishop against a king surrounded by his own unused pieces. Teachers like it because a beginner can follow it on the first reading and an experienced player still finds something new on the tenth, usually in the order of the moves rather than the moves themselves.

The order is the hidden subject. Morphy's thirteenth move takes a knight with a rook when the bishop could have taken it. That choice keeps a pin alive for one more move, and the whole finish depends on it. When you watch the game with someone new to chess, that is the moment to slow down. Ask why the rook, and not the bishop. There is a real answer, and finding it is more fun than being told.

What is known, disputed and legendary

• Known. The moves, all thirty-three of them. The players. The place, a box at the Italian Opera, and the season, autumn 1858.
• Disputed. Which opera was being performed. Edward Winter's review of the newspaper evidence in Chess Notes gives Norma in late October or, most probably, The Barber of Seville on 4 November 1858. Nobody wrote it on the score sheet, so the argument continues.
• Legend. That Morphy sat facing the stage, half watching the singers. It is told in many books and recorded in none that settles it.

That last line is worth slowing down for. A story this good attracts details, and details that fit a story feel true. The habit of sorting what you are told into known, disputed and legend is the same habit whether you are reading about a chess game, a news story or a family anecdote.

How a disputed detail gets settled, or doesn't

It is worth knowing how the opera question is argued, because the method is more useful than the answer. Historians of chess do what historians of anything do. They look for sources written at the time: newspaper notices of what was playing on which night, letters, the first published versions of the score and what they said about the occasion. Then they weigh them. A detail printed the week after an event counts for more than one printed fifty years later. A detail that appears only in later retellings, growing more vivid each time, counts for less.

By that method the moves are as solid as anything in the history of the game: they were published early and have never varied. The night at the opera is less certain, because nobody thought to record it alongside the score. And the picture of Morphy watching the stage rests mostly on retelling. None of this makes the game a worse story. It makes it a better example of how to hold a story: firmly where the evidence is firm, and loosely where it isn't.

The question for the table

If you play through the game with a child, stop after Black's fourteenth move and ask: "Whose pieces are helping right now?" Count them together. Then ask the harder one: "What would you give up to get the rest of yours into play?"

Your child may have just read the same game in a different form, as The Opera Game at the Slow Lake Academy, where each move belongs to a character whose tactic it is. In that version a girl named Inkling has to work out who steps up next. You may find you are asking each other the same question.

Something to do

Play the last five moves together, from the position after Black's twelfth move. Let the child take Morphy's side. If they find the queen sacrifice on their own, do not tell them it is the famous move. Let them find that out later. If they don't find it, play Morphy's moves yourself, slowly, and say out loud what each one is for. Children often remember a game better when a grown-up has been visibly surprised by it.

Thinking in Odds, the Whetstone course, takes the same approach to dice. This one takes it to development. Neither is really about winning games. Both are about noticing what you already have and are not yet using, at the table and away from it.