Exceptions to Castling

Now, castling is not infinite: it cannot happen at any time. There are certain rules that determine when you can and cannot castle. In fact, remembering and understanding the exceptions for castling is almost as important as understanding castling itself.

Here are the exceptions to castling:

1. You cannot castle if you King has already moved.
2. You cannot castle if your Rook has already moved.
3. You cannot castle if you are in check.
4. You cannot castle if you move through check or end up in check in the process.

Let’s examine all these rules one by one.

Rule 1:
This is a fairly simple rule. Let’s see this in action first, and how people might try to “cheat” castling.

Here is the position: it’s White’s turn, and he is debating on whether to castle or not. Can he?

The answer is no: since the king has already moved from the e1 square, he cannot castle.

Rule 2:
Same content as the previous rule, but this has to do with the rook.

It’s White’s turn. Can he castle Queenside?

The answer is no: since the rook is on b1, he cannot castle Queenside. He can castle Kingside though, since the rook has not moved yet.

Let’s look at a final example, to see how the two relate to each other. The moves aren’t good, but they do help to set up this example. Keeping that in mind, here is the position:

This is the position, and it’s White’s turn to move.

1. Kd1 Kd8

White makes a curious move, and Black follows suit. This is the position now:

2. Ke1 Ke8

Here is the position:

Have you noticed something? This is the exact same position as from move one – but the difference is that the kings moved! Can white castle next turn?

The answer is no. But why is this?
Read rule one carefully: you cannot castle if you King has already moved.

Despite the last example visually being the exact same position as last time, the King moved: so therefore White cannot castle.

Rule 3:
Now, let’s move onto the other rules that deal with check. They’re relatively simple, but it’s still important to review nonetheless. In this case, Rule 3 refers to the fact that you cannot castle if you are in check. Let’s see this rule in game:

Last move, Black moved his rook to e8, checking White’s undefended king. Since White is in check, he cannot castle out of it. He can move his King to fl, dl, or d2, but he cannot castle.

Very easy! Now, let’s move on to rule 4, which requires a bit more practice to understand.

Rule 4: Rule number 4 states that you cannot castle if you move through check or end up in check in the process. Don’t worry if this seems confusing at first, we’ll look at some examples. In the position below, it’s White to move, and he’s contemplating on whether to castle or not. Let’s see if he can. e

Let’s look at all the castling methods without a visual aid first. Firstly, let’s look at the 2 options, castling Kingside and Queenside. It’s easy to see why castling Kingside at first doesn’t work: the bishop covers the square that the king ends up on (g1). So, if White castles, he would be ending up in check, which is illegal.

Now, let’s look at castling Queenside. On first glance, it appears to be alright: White doesn’t end up in check on the c1 square.
However, in castling, he moves through a square that the black rook covers: d1. A “covered” square (dl) on the path to Queenside castling prevents White from castling. Therefore, White cannot castle on either side, and is advised to find another move.