Is it necessary to know all three types of writing?
As I'm sure you know, Japanese has three writing systems: Katakana, Hiragana, and Kanji. But is it necessary to know all three? Is it okay to just know Hiragana, or just Katakana, or just Kanji? Your answers are much appreciated!
You'll want to know all three, at least on sight. Knowing how to write kanji out by hand is less essential than it used to be, because keyboards will allow you to type in hiragana and romaji and will turn those into kanji for you. But, you'll need to be able to recognize it if you plan to read anything in Japanese, likes books, manga, street signs etc. There is basically kanji everywhere, minus books written very very young children.
Hiragana is important because it is often paired with kanji. In Japanese, verbs conjugate, but everything else has declension. For instance, if you are talking about a red thing, you are also talking about the time frame of the red thing. Is it red now? In the past? If it wasn't red in those time frames, will it be red in the future? Also, Japanese particles are written in hiragana.
Katakana is useful when it comes to reading loan words. So, words like "Pizza" will be written in katakana if you are reading a menu. Also, older documents are written in katakana. Once upon a time, katakana was used more often than hiragana, and not just for loan words.
Of the three, katakana is probably the least important. But, ultimately you'll want all three.
(Many thanks to Michael.Lubetsky's comment below, correcting my impression than katakana was less essential.)
With respect, I am not sure I agree with the comment that "katakana is probably the least important". Some 90% or more of words written in katakana are loan-words from English. When I first arrived in Japan, words written in katakana were the only ones I could understand -- I would zero in on them on signs and (especially) on menus! In Korean, by contrast, there are also English loan-words, but they are written in Hangul and don't stand out obviously.
Of course, if you know only katakana, you will really only be able to read the English loan-words, which is useful for day-to-day survival as a foreigner in Japan but won't get you very far in building proficiency in Japanese.
If you know only hiragana, you will be able to read children's books. That's about it.
If you know only kanji (actually not uncommon -- think of all the Chinese people who come to Japan), then you will be able to understand signs and probably get the gist of lot of advertising. You won't necessary know how anything is pronunced.
Bottom line: You gotta know all three systems. It really isn't as bad as it sounds, since because of hiragana and katakana, you need to know fewer kanji. To be literate in Chinese requires knowing about 5000 characters; Japanese requires less than half that.
Frankly, you can function pretty well in Japan with much fewer characters. I found a book in Japan that identified the 206 most commonly-appearing characters, that apparently make up an astonishing 50 per cent of all character usage in newspapers. I applied myself to learning those ones and my literacy skyrocketed.
By the end of grade 6, Japanese schoolchildren are expected to have mastered about 700 kanji (called the 'kyoiku kanji")....and virtually all of them do.
Yep. ^^ I'm at the stage where I can read something like 2,500 kanji already anyway. Though I've not learned Chinese, my understanding is that there is considerably less trouble involved learning each hanzi compared with the messier situation of kanji.
The two kanji frequency lists on this web page are pretty interesting: https://foosoft.net/projects/kanji-frequency/
I added up the frequency percentages of the most frequent characters to see how many one would need to learn to reach 50% coverage in each of those two lists:
The "text from hundreds of novels" report contains 5,517 kanji. Yet the top 187 most frequent of these account for 50% of the kanji usage.
The "Wikipedia" report contains a staggering 20,932 kanji. Yet just the top 139 most frequent of these account for 50% of Wikipedia's kanji usage!
Those two frequency lists probably aren't so great to go by though. The Wikipedia one is pretty skewed towards certain kanji that appear on every Wikipedia page by default. The 3rd and 4th most frequent kanji in its list are, ridiculously, 編 and 集, thanks to the word 編集 ("edit")... ^^;
Also, about the kyōiku kanji list, doesn't it have, more specifically speaking, 1,006 characters?
Thanks for that link. It illustrates well the point that learning about 200 judiciously-chosen kanji will give you a good measure of literacy. There is no reason to frighten learners with numbers like 2000 or 3000!
Wikipedia says that you are right about the number of kyoiku kanji; I stand corrected! :-)
Knowing only hiragana is enough to pass the JLPT N5 test however it won't help you in any way when dealing with real Japanese. Knowing all 3 scripts is pretty much necessary to understand anything in N4-N1 tests or real life. Also, ironically Kanji make reading Japanese much easier
Learning kanji is a challenge, but it's a fun challenge. I recommend learning the 2,000 or so jouyou kanji. Different people have different methods of learning kanji. Heisig's Remembering the Kanji has been effective for me. Also, Anki will be your friend. A lot of no-nonsense Japanese learners use it, so there are Japanese decks to choose from.
Good luck, and have fun. It will open up an amazing world.