Principles explained #2 - Why do we castle?

There are a lot of chess principles we hear all the time, but don’t necessarily understand, or never really investigate. The purpose of these posts is to take a closer look of those principles, and examine the logic behind them. 

One of the first things you must have learnt as a beginner that you should always castle in the opening. It is very sensible advice, and for a beginner, it makes a lot of sense to follow it without much thinking; but there comes a moment when you have to re-evaluate this advice a little bit. Just like the other principles of chess, the principle of castling should not be applied blindly. 

So - why do we castle at all?

We castle for two reasons: to make the king safer and to develop one of the rooks. (By the way, it is a common mistake that people only think about the first reason and forget about the second one.) 

Why is the king not safe in the middle?

When we  fight for the centre in the opening, we tend to exchange at least some of the central pawns; and as a result, there will be open files in the centre. These open files make the middle of the board dangerous for the king, but at the same time attractive for the rooks. Therefore castling usually means killing two birds with one stone: making the king safer and improving at least one of the rooks. 

There are cases though, when castling is not so obviously beneficial. Let's look at them.

1. Bringing the king to unsafety - for the sake of the rapid development of the rook.

This is one of the classic dilemmas - so let's see a classic game from Blackburne to illustrate it.

Did 9. 0-0-0 make the white king safe? Not really - the king would have been much safer on the kingside, but White sacrificed king safety for rapid development. As everything in chess, the king's safety can be subject of a trade-off. (Well, to a certain degree, of course.  )

2. Leaving the king in the middle in order to use the rook on the wing. 

Another typical dilemma - what if the rook can be used better at its original place, and castling would actually undevelop it? A few examples:

3. When the safest place for the king is the middle

Here is a famous example from Artur Yusupov. Black could have castled both side, but he simply decided that the best place for the black king was in the middle:

Please note: I am not trying to dissuade you from castling in general. In most games, castling is the simplest and quickest way to make your king safer and improve the position of your rook. But you should be aware that there are plenty of exceptions, and you should not castle all the time mechanically. As Pillsbury put it: " Castle if you will or if you must, but  not because you can."