What is the four-move checkmate?

1.e4 e5 2.Bc4 Nc6 3.Qh5 Nf6 4.Qxf7 mate, known as Scholar's mate. The bishop on c4 and the queen on h5 both attack f7, which the black king is defending on his own. When the queen captures there, the bishop protects her, so the king cannot take back and has no square to run to.

Does the move order matter?

Not for the mate. 2.Qh5 Nc6 3.Bc4 and 2.Bc4 Nc6 3.Qh5 reach exactly the same position. It matters a little for the practical chances, because 2.Qh5 attacks e5 straight away and forces Black to answer, while 2.Bc4 looks like an ordinary developing move and is easier to fall asleep against.

What should Black play instead of 3...Nf6?

3...g6 attacks the queen and blocks the diagonal in one move, and 3...Qe7 gives f7 a second defender. Both are good. 3...Nh6 also holds, though the knight ends up awkwardly placed. What loses is any move that ignores f7, and 3...Nf6 is the most tempting of those because it develops and hits the queen.

Checkmate in 4 moves

1.e4 e5 2.Bc4 Nc6 3.Qh5 Nf6 4.Qxf7 is mate, and the bishop on c4 is the reason the black king cannot take the queen.

The bishop-first version of the four-move mate: 1.e4 e5 2.Bc4 Nc6 3.Qh5 Nf6 4.Qxf7 mate.

Two move orders, one position

Most people are taught 1.e4 e5 2.Qh5 Nc6 3.Bc4, queen first. The bishop-first order above transposes: after three moves both give a queen on h5, a bishop on c4, a black knight on c6 and a pawn on e5. Same position, same mate.

The difference is psychological. 2.Qh5 attacks the pawn on e5 and announces itself, so Black has to think. 2.Bc4 is a move Black sees in the Italian Game every day, so the alarm does not go off, and the queen arrives on move three against an opponent who has stopped looking.

Black to play. f7 is attacked twice and defended once. Find the defence before you read on: 3...g6 or 3...Qe7 both hold.

Why 3…Nf6 is the losing move

Because it is the move a well-taught beginner wants to play. It develops a piece, it fights for the centre, it attacks the enemy queen. Three of the four things you are told to do in the opening.

It fails on the fourth thing, which is that a threat of mate comes before everything else. Nf6 does not defend f7 and does not block the h5 to e8 diagonal, so White simply takes and it is over. Do the arithmetic on f7 rather than admiring your own development, and the move plays itself: 3…g6 hits the queen and closes the diagonal at once, or 3…Qe7 puts a second body behind the pawn.

The day it stops working

Somewhere around your fiftieth online game, and I would not be sorry to see it go. Once your opponents answer with 3…g6 you are left with a queen that has to move again, a bishop on c4 that will be hit by …Na5 or …d5 at some point, and nothing developed on the queenside.

There is a fuller account of the defences and the cost on the Scholar’s mate page. The healthier place to put this energy is a trap that arises out of a normal opening rather than instead of one: Légal’s mate needs no cooperation beyond greed, and the pattern of piling on f2 and f7 keeps paying off long after the four-move mate has stopped.