Checkmating with a Knight

One of my readers, Phil, has asked this question: Can i win with a knight and king against a king?

The short answer is, “no.”

The long answer is a little more interesting, and has a surprise in it. First, let’s look at what happens when you try to checkmate a lone King with a King and Knight.

King and Knight can’t checkmate a lone King.

In order to checkmate the enemy King, you must, at a bare minimum, be able to check the enemy King when he is in the corner of the board and cover the three possible escape squares. So let’s say that the Black King is sitting on h1. Since the King can’t check the enemy King (the King giving check would also be in check himself), the check must be delivered by the Knight. That means that the Knight would have to check the King at h1. So the Knight would have to sit on f2 or g3. Let’s imagine that the Knight is on f2 and delivering check to the enemy King at h1. Like so:

Now we just have to add the White King to cover the possible escape squares. If we put White’s King on h3 or g3, it covers two escape squares (h2 and g2), but it leaves g1 open.

And if we put the White King on f1 or f2 to cover the g1 square, that leaves h2 open as an escape hatch. As it turns out, there is no way to cover the four squares needed to construct the checkmating position. There is just no way to make a position where the King and Knight can checkmate the lone enemy King.

If you doubt me on this, I encourage you to get out a chess board and try to set up a checkmate position. It can’t be done.

But the King and Knight can sometimes mate the enemy King.

Here’s the surprising part: the King and Knight can checkmate the enemy King in certain positions if we give Black a little more material — i.e., where Black has a Rook-pawn.

First, you should know that this is merely theoretical; it will almost never come up in a real game. (Reuben Fine called this a “problem position.”) But it is helpful to know the idea, if only to know how the pieces react with one another. So here’s the idea.

In this position, White can checkmate the enemy King with two beautiful moves:

• 1.Nf1 (stalemating the Black King, and so forcing his next move)
• 1…h2
• 2.Ng3 mate

Beautiful, isn’t it? But let’s make the position a little tougher. Let’s change the starting position of the pieces so that the White Knight starts at f4, like this…

… we actually have a mate in 6. Check this out!

• 1.Ne2! Kh2 (otherwise White will play 2.Ng3 mate)
• 2.Nc3 (White could also play 2.Nd4 and then 3.Nf5 here) Kh1
• 3.Ne4 Kh2 (Again forced, else White mates immediately)
• 4.Nd2 Kh1
• 5.Nf1 h2
• 6.Ng3 mate

Speaking of Stalemate

It is possible to stalemate Black with a King and Knight. In this position, for example:

White is two moves from checkmate, and wins with either 1.a8(Q) or 1.a8(R) or any other move (though other moves would take a little longer) except for one: 1.Nf3?? stalemate.

It would be better in this type of position to get the Knight out of the way, forget about it, and just win with the Queen and King against King. If you need to review the procedure for checkmating with a King and Queen against King, just click the preceding link.

So there you have it, Phil — you can’t win with a King and Knight against a King. But I hope it turned out to be a little more interesting than you thought at first! 🙂