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Visit Hacking Chinese instead: This post about studying Chinese is partly or completely obsolete. A revised version, along with much more related to language learning can be found at Hacking Chinese. This post is kept here for the sake of consistency.

Update: Much of what is written in this article is irrelevant or obsolete, even if the underlying arguments are still valid. I no longer use the ZDT software, but have changed to Anki, which is superior in almost every regard. Check it out if you haven’t already!


There are many tools out there which will greatly facilitate learning Chinese (I’ve discussed some of them here). For various reasons, I’ve been using a program called ZDT (Zhongwen Development Tool) almost from the start, which is about two years now. The program isn’t perfect, but it’s by far the best I’ve found, mainly because of one single function: the interval filter. This post is not meant to be a review of the program or its functions, but rather an attempt to explain why this filter is the best thing since sliced bread and how I use it in my everyday learning. I realise that a general post about ZDT would be a good idea, but I’ll leave that for later.

In ZDT, each vocabulary item has some data attached to it, most importantly how many correct and incorrect answers you’ve had for that specific word and when it was last checked in a flashcard session. The interval filter is very simple in its basic function: it simply looks at each character and determines how well you know it (based on the balance between correct and incorrect answers), and then checks when you last reviewed it. Depending on how well you know a word, the program will then determine if it’s time to review it again or not, everything based on your familiarity with the card (again based on test record).

Benefits of the interval filter

Correctly set-up (more about that later), the interval filter is all you need to expand and maintain vocabulary. Let’s take a look at that sentence again: the interval filter is all you need to expand and maintain vocabulary. Yes, I’m serious, I hardly use anything else. How is this possible? There are two areas in which the interval filter proves its usefulness.

First, when studying a new chapter, I simply enter all the words into a new category and immediately start a new flashcard session for that category (no, I haven’t made an attempt to learn the words first). What will happen now is that some words I will know from before without having to study. These are sorted out and won’t return for another 24 hours (see about tweaking the filter below). The rest of the characters automatically get -2 points because I don’t know them. When they appear, I study them carefully, perhaps looking up radicals, composite parts and whatever. At the end of the session, these words come back and usually I’m able to nail around 90 % of them the second time around, which means they end up on -1 point each. The remaining cards will have even more minus points depending on how many rounds you need to finish them off. Repeat this at least once within the first day. Note that this will leave you with flashcards ZDT thinks you ought to study now (some had -1 or less, which means you need more than one session to bring them to a positive value), and even if you do two more session the same day, some will still have a negative score and thus appear in the test. This is fine.

The next day, all characters will return again, even those you answer correctly the first time. This is essential for long-term retention. Most of the rest won’t be a problem, but some characters or words always persist and seem impossible to learn. Don’t worry, these will retain a very low score and you will be harassed by them once or twice every day until you know them. The characters will slowly advance up the ladder and out of the way, occurring more and more infrequently. Thus, the only thing you need to do is do at least one ZDT flashcard session every day, but two might actually work a lot better because it will the decrease the load and make sure you get the really difficult ones more often.

Second, the interval filter is perfect for revising old characters and words (this is rather obvious and probably the main reason why it was created in the first case). You never ever have to care about which words to review, you seldom have to waste time studying words you already know. Most other revision methods will force you to check ten words you already know for every word you actually need to study; the interval filter greatly reduces the time you thus waste on things you already know. It makes it possible to remember all the words you’ve ever learnt, without putting unreasonable strain on you.

How to use the filter

If you’ve just started studying Chinese, well, congratulations, the transition to using a filter like this is painless. When you have time, simply select all the categories you have and start a flashcard session. Do that as often as you can, keeping the characters you need to review at zero. If you’ve been studying Chinese for a long time and have thousands of words, it’s a lot tougher. I would suggest gradually moving over to a time interval system, but you might have to open the ZDT file containing the words and manually alter the points for your old words and start out at level higher than zero. Having 5000 characters all starting from zero would be an insurmountable obstacle, so don’t do it.

This method currently has one drawback, and that is that in ZDT, you can’t distinguish between different kinds of flashcard sessions. For instance, the program scores a pinyin recall test in the same manner as a self-review test. My own solution to this problem is to use two separate “super categories”, one for characters I want to be able to write (i.e. all characters in the Practical Audio-Visual Chinese series) and another for those I’m satisfied if I know the meaning and the pronunciation of. Then I simply run self-review for the first section and pinyin recall for the second. This isn’t perfect, but it has worked fine so far. I currently have 3200 and 3600 flashcards respectively in these two categories and this is probably the only way to handle such a large quantity of words.

Tweaking the filter

The filter can of course be tweaked, which is what I’m going to talk about now. First, the points you gain or lose for correct or incorrect answers can be altered. The default values are 1 point and 2 points respectively, and I see no serious reason to fiddle with these numbers. The reason the penalty has to be 2 and not 1 is that the character will return at the end of the test, which means that you will always get at least one correct answer. Changing both values to 1 would therefore mean that you can never lose points unless you answer incorrectly twice in the same session, which isn’t very likely.

Then there is the intervals themselves, and I recommend changing these frequently in the beginning to gradually find ranges which suit your learning curve. For instance, if you find that you continuously run in to characters you added a week ago, but that you never answer correctly, you have to change the intervals in the lower range of the spectrum. If you find that old characters which you know intimately keep bothering you although you never answer them incorrectly, you need to expand the intervals in the upper range. I have tweaked a lot and I currently use 1, 1, 2, 4, 7, 11, 20, 35, 50, 75, 100, 150, but this is of course no guarantee that it will work for you.

Conclusion and discussion

The ZDT interval filter is indeed the best thing since sliced bread and it is a marvellous tool for learning Chinese. I can envisage few other ways of building a solid vocabulary base (a friend uses a sort of manual interval filter with physical flashcards, but that seems too impractical when you reach several thousands of flashcards). I think many people use ZDT or other similar programs without realising the potential of the tool they’re using, something I hope to have changed at least slightly by writing this article. If you have any feedback, please post a comment. I would especially be interested in other people’s values for the intervals, provided you aren’t using the default ones, but any constructive feedback is more than welcome. Thanks to Chris for a wonderful program and thanks to you for reading this!

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Visit Hacking Chinese instead: This post about studying Chinese is partly or completely obsolete. A revised version, along with much more related to language learning can be found at Hacking Chinese. This post is kept here for the sake of consistency.

Update: This article was written a long time ago, so even if most of what I say here is still relevant, I have developed my revision strategy a lot. Check this post for some ideas.

This article is the third part of three concerning the study of Chinese. I have composed these articles for various purposes, but mostly because I enjoy writing. I also feel that I have something important to share, and even though I am sure that others have written about the same concepts elsewhere, this is how I view it. Hopefully, these ideas will be helpful to other students. Another reason for writing these articles is that I want to show those of you that do not study the language a little bit how I feel and think about Chinese. These are the three parts:

Part 1 – Attitude
Part 2 – New characters
Part 3 – Revision

Learning Chinese characters – Revision
Having read the first two posts in the this small series of articles, one might draw the conclusion that learning what a character means and how to write it is the most difficult and time-consuming part of studying Chinese. This is wrong in every repgard. The really difficult bit of studying Chinese is to have the discipline and time to revise what one has already learnt; in other words, not to forget what the first two parts of this series focused on. Since this is a problem that increases with one’s knowledge of the language, it is also something I personally feel is very important to discuss. Remembering how to write a character is a real problem for native Chinese as well, especially for those who do not write by hand as a part of their daily lives. Writing using a computer merely requires one to know how a character is pronounced and what it look like, which is not the same as being able to write it by hand.

That being said, I have used trial and error to find a suitable revision method (admittedly, after studying languages for many years, I had a good idea of what I wanted before). My original intention was to publish this article in close succession to the previous two parts, but I began altering my revision strategy at the same time, so I decided to wait until that change was fully implemented. What I present here is by no means based on any serious research, but it is founded on my rudimentary knowledge of psychology and a lot of consistent blood, sweat and tears.

Committing characters to long-term memory
If the disposable time was unlimited, it would probably be best to keep track of sets of characters (such as from a chapter in a book) separately and make sure that any given set of characters was revised occasionally. However, time is painfully limited and for reasons I will explain in the next section, I have come to the conclusion that two separate systems are needed for revising characters. What I will say about the initial phase, committing characters to long-term memory, is based on my own revision schedule, which looks like this:

Click for higher resolution image.

It is difficult to analyse this kind of data without proper software or knowledge, but basing my writing on feeling, reflection and studying of the chart above will probably get me somewhere. The blue boxes are checks from pinyin to characters using ZDT. This is by no means anything fancy, it just means that I go through all the characters in a random order and make sure I know how to write them. If I do not remember how to write them or write them incorrectly, I count that as an error and continue with the rest. After one round, the incorrectly answered characters appear again, and normally I have no problem the second time. Later, I repeat this procedure for the same chapter, noting the number of correct answers (the figures in the blue boxes). The most important question here is of course how often to do this in order to optimise retention.

If working with simple repetition (which is a fairly poor sort of revision anyway), the human mind works in a rather predictable pattern. The most important thing is to find out what that pattern is like for a given learning situation. I have found out a couple of truths about how my brain works when it comes to revising characters, and I am pretty sure than most of them are applicable to other people in other situations as well. Here is what I have found out about revision intervals:

As I have already stated, I do the initial learning in the evening, and the first revision session is directly afterwards. Once I have studied each and every character carefully (as described in the second article), I simply read through the list of characters, refreshing my mnemonics and making sure I know what the various parts mean. This is often done very quickly.Then I go to sleep. Immediately upon waking (or very soon thereafter), I carefully go through the list again, using a pinyin to character test again. This is not done in a hurry, but I actually make sure that I can write all the characters. Usually, I am able to remember between 80 and 85 percent of the characters from the evening before.

Then I do not touch the characters for the remainder of the day, or if I do, I just quickly skim through the list on my mobile phone waiting for the bus and suchlike. The next revision session is the next day (the third day since, counting the initial learning as the first day). It does not seem to matter when during the day I do this, but it has to be done the third day. After than, I should revise again on the fifth and eighth day, which usually leaves me with a score seldom below 95 % and often close to 100 %. Even if i do not revise further, I can usually remember how to write more than 95 % of the characters several weeks after the initial learning (see the first article for a discussion about how good is good enough). If I realise that I have a problem with specific characters even after this time, I put them in a separate category so as to be able to practice them without having to go through the entire chapter that contains them. This is obviously saves a lot of time.

In summary
Day 1, initial learning in the evening
Day 2, revision in the morning
Day 3, revision
Day 5, revision
Day 8, revision

Future revision and retention of characters
Even if the aforementioned procedure leaves me with a satisfactory 95 % knowledge of the characters in any give chapter, even weeks after the initial learning, this does not mean that the understanding is permanent. If characters were left unused and unrevised, I have no idea what the curve showing loss of writing ability to time would look like, but I am pretty sure it would be an unpleasant affair, so let us instead make sure that they are not left unrevised.

As I mentioned in the first article, it should also be noted that the goal is very important. Is it necessary to have 95 % retention or is 90 % or even 85 % satisfactory? The relationship between percentage of correct answers and time spent on revising is exponential, so think carefully about this one.

Before I go on to explain why I think a computer is an essential and powerful tool to study Chinese, I will discuss the problem that faces all those who study foreign languages, namely that of effective revision (so far I have only dealt with intervals, not how one goes about the actual revision). Simply using a text book to revise is abysmally ineffective, because it means that too much time is spent on revising vocabulary that does not need revision. Imagine, for instance, a chapter where I know 95 % of the characters and need to revise 5 %. Studying the entire chapter is a waste of time, time that could be spent on revising other characters or learning new ones.

This is where the computer comes in handy. As I have already said, I use ZDT for this, but I do not doubt that there is a plethora of programs out there on the web capable of doing the same thing. I will use ZDT as an example simply to explain what I mean. The key feature is what is called an interval filter. Running any of the various flashcard checks in the program, this filter adds X points to a flashcard each time the user gives a correct answer, and deducts Y points every time an incorrect answer is given. X and Y are of course parameters set by the user. Furthermore, there are parameters for every given value of the sum X and Y, in other words, the current score for a certain flashcard (a high value meaning that correct answers are frequent). These parameters govern how often a flashcard is shown if the interval filter is enabled.

Why is this so marvellous? Because, provided that the interval filter is set up correctly, it means that it is possible to only focus on the characters that really need revision. If a character seems to be easy (many correct answers), it will appear less and less frequently, until at last almost never. If the character is difficult, it will keep appearing very often until the number of correct answers increases. Likewise, if an old character is forgotten, its score will tumble and it will appear more frequently until it is mastered once again. This is impossible, or at least extremely impractical, to do without a computer. It will save a lot of time, even including the fact that it takes time to key in the characters in the first place (please note that wordlists from many text books are provided by users, including myself, on the ZDT page).

That being said, simple repetition is a poor revision method. It will work for many characters, but if I feel that some character is refusing to lodge itself in my long-term memory, I will change method for that character. Here are some ways of learning difficult characters:

– Create a sentence of your own
– Find a better mnemonic
– Draw a picture
– Count the number of strokes
– Check the various parts again
– Check etymology
– Look at other words including the character
– Read the source text

The only thing that is required apart from a system like this is diligence over time, which of course is extremely difficult, but which is something I will not even try to approach in this article (even though I have written about related topics here and here).

Revision in context
Perhaps this ought to be the topic for an entirely new article, but I feel that my writing about learning Chinese is beginning to spin out of control, so I will try to keep it short. In essence, the best (and perhaps only) way to learn a language is to follow up studying by revision in context. By this, I mean that it is necessary to encounter the characters or words in context a couple of times before being able to use them properly. Simply studying a text book and grammar will never instill the feeling for the language which is necessary for a high proficiency. Obtaining this feel is only achievable through reading and listening a lot. And when I say a lot, I mean a lot. I am sorry, but there are no shortcuts, no smart strategies or other ways to help; spending perhaps thousands of hours immersed in the language is the only way.

By way of conclusion, I would like to invite everybody to some sort of discussion. Have you thought about the topics for these three articles and have you related them to your own situation? Have you some experience you feel is relevant for what I have said or do you just want to voice your opinion? Perhaps you even have pertinent scientific material or references to share? Whatever it might be, please, go ahead and post a reply.

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Occasionally, a debate flares up on the subject of whether to allow changes to the 101-in-1001 list or not. In this post, not only will I comment briefly on the changes I have done, but I will also try to provide some sort of rational ground for doing it.

First of all, let us consider the purpose of starting a list. I realise that different people have different goals, but my goal is making sure I do things which I want to do. For many years, I have been fascinated by this tendency of human beings to avoid doing things they actually like doing once they get started, and creating lists is one way of giving a decisive push in the right direction. In some ways, it might be regarded as attempting to lift oneself by one’s bootstraps, but since it seems to have practical effect, I am inclined to postpone the bootstrap debate until some other time.

I also think that it is much more enjoyable to finish something in its entirety rather than just partly, so I perceive an increased chance of finishing tasks on the list if a 100% success is still within reach. I regard failing with one task to be a catastrophe, but failing with two would not be very much worse, certainly not twice as bad.

That being said, what hinders me from changing all the difficult tasks into something manageable? Doing that would contradict the whole purpose of the list. I realise that writing a novel will take time and will be difficult, but it is something which I would like to do, and so the task remains. We have now arrived at the crux of the matter, I only keep tasks on the list which I want to do. The list was (before this update) rife with tasks I had not really thought about enough or tasks which are simply not relevant any longer.

For instance, when I first created the list, I was fairly into Tai Chi Chuan, which naturally led me to come up with a number of tasks related to that. Now, more than a year later, I have quit practicing because I have found other things to do in my spare time, which suit me better. Thus, two points were removed. However, I kept the “Do 4004 Nei Kung exercises, at least 4 each day”, simply because that is something I still think is worthwhile.

This means that I am not prepared to remove a task because it is too difficult or because it takes too much time, since that would, as I have already stated, invalidate the core idea with the list. I do not shy away from difficult or demanding tasks, but I do shy away from spending time on things which I no longer want to do. It seems stupid and counter-productive. Keeping such tasks on the list would create confusion, because I would have the goal of finishing the list at the same time as I insist on my being stupid in doing so (since it would involve spending time on things I do not enjoy).

Conclusively, let me say something brief on the update of the list. I have removed approximately ten tasks, added another ten to replace them and finally changed about twenty, in most cases with the intention of increasing preciseness of formulation and not of altering the intended task. In doing so, I also had to remake the numbering of all the tasks, and thinking that I might as well take the opportunity, I rearranged the categories a bit, making the list more navigable. So, feel free to visit my updated 101-in-1001 list and wish me good luck with the remaining 80 tasks. If you spot any mistakes or errors, please notify me.