This is just my two thoughts on a debate that has people arguing on all sides of it. Basically, the question is this: should switching to a monolingual dictionary be a goal to set? I can see why people would think it’s beneficial, but in my personal opinion, I don’t think this should be a goal. For one it’s boring, and for another I don’t think it motivates as well as reading actual books.
There are a number of language learners out there who say, “After X many words, I’m switching to a monolingual dictionary!” I could be wrong, but I’m assuming people want to do this because somehow understanding a dictionary indicates a high level of reading, or maybe because they think it’ll motivate them to memorize whatever number of words they have in mind. I personally don’t think the ability read a dictionary is very indicative of skill, though.
So, here’s why I don’t think that making the switch to a monolingual dictionary should be a priority, although I have no problem with people using them.
1. Dictionaries are tools, not goals. Like all tools, use what’s easy for you and useful at the same time. Sometimes a monolingual dictionary will convey meaning better than an English-Japanese/Japanese-English dictionary will, but most of the time I still use a bilingual dictionary. Use what’s handy to you, and bilingual dictionaries are great tools for a lot of things.
Your goal should be to do what you want in Japanese, whether that’s reading manga, watching j-dorama, or talking with people on the street – it shouldn’t be to read a dictionary, unless you really love dictionaries. So, use your dictionary as a tool for learning new words, but don’t make it a goal, as though it indicates a new level of Japanese.
2. Monolingual dictionaries don’t represent your level. Reading real Japanese as found in books and things is much more representative of your level, and using a bilingual dictionary doesn’t mean that you can’t read Japanese well – it just means that it’s the tool you prefer.
I primarily use a bilingual dictionary for Japanese, unless it’s obvious that the definition covers more than the English equivalent, if there even is an English equivalent. That’s not to say that my Japanese is weak, but I just don’t get the love and desire to switch exclusively to a monolingual dictionary.
On the contrast, my Italian is a bit poor, but I use a monolingual dictionary for Italian. Why? I don’t know. It’s personal preference, I guess.
3. Reading books is a better way to expand your vocabulary. When you take an English class, how does your teacher tell you to increase your vocabulary? Most of the time, he or she will tell you to read. Anything, at that. Just keep reading and the vocabulary will come to you. This is the crux of sentence mining and why it’s a popular way of learning Japanese, or any language for that matter.
Now, some people prefer to expand their vocabulary by looking up one word in the dictionary every day and attempting to use at some point in conversation. This is great, except that it seldom works in the long run. You’re better off exposing yourself to the word as often as possible.
Now, I don’t think it’s bad to use a monolingual dictionary if you’re comfortable with it and feel that you get more out of it than you do with a bilingual dictionary. I just don’t think this should be a priority, or a step in your ultimate goal. Use tools as tools, not as the end-all-be-all.