Memorize Things Based On Their "Replay Value"
This is a continuation/extension of my earlier post, Memorization and why it's good for your chess but can be read as a stand alone article.
Many people have the impression that we memorize a lot of things in chess. Other people think that we should not memorize anything in chess? Who is right? As expected, it must be the middleground.
How do we determine what should be memorized?
We can start by discussing what should not be memorized. Tactical puzzles, positional puzzles, or similar things of that sort should not be memorized. This is because it is unlikely to see that exact position again. Make the effort to know and learn the theme - but it is hard to understand what could be the value in putting the exact position into memorization. We tend to find these puzzles in positional or tactical puzzle books.
Now that we have defined replay value to be the probability that you will have to use something again, we can give some examples of what should be memorized:
This one might be a bit controversial. Many, many people say that openings should not be memorized and that we should only learn the concepts. Yet I am saying that they should be memorized. Well, both are right, it has to do with your goal of opening study. If you are studying the opening just to get a feel and start playing it immediately, then learning the concepts is sufficient.
But if you are learning the opening to make it one of your main weapons and become a specialist in it (you know you are one of these people if you are spending significant time on openings and/or are using an opening book) then you must memorize the lines you are looking at. An easy way to do this is to do some sort of "guess the move" where you cover up your moves and see if you can find the right reply for each move. As a greater challenge, can you recite the lines without looking at the moves at all? (just write down the notation on a piece of paper)
If you can't do that, then that guarantees that you will not be able to do it in a tournament game. Then what's the point? If you're going to invest significant time to opening study, then make sure you can qualify the progress!
We must define the goals here, just as we did above for openings. Endgame study tends to divide itself into "technique" and "theory." Technique would be very conceptual, like "do not rush." In these cases it is useful to know the concepts.
Theory is how most people study endgames. These involve "lucena" or "philidor" or "wrong rook pawn" etc. These must be known by heart, we are very likely to see them in tournament practice! What you decide to memorize is up to you, for some of these we should know the exact moves by heart, for others it is sufficient to just memorize the key positions (e.g. "if we are left with pawns on h2 and h3 then it's always a draw as long as our king is in the corner )
There are many other cases where memorization is warranted, but I do not have enough space to list them all here. But using the idea of replay value, you should be able to figure out which things fall into this category!
I hope this post helped, and if something didn't make sense please ask in the comments below. By no means am I saying that we should invest a major portion of our study time to memorization, but that time we do invest we must make sure we do it right.