Kanji and radicals

The Japanese writing system, as it happens, was basically stolen from the Chinese. You see, for a long time the Japanese had a SPOKEN language, but not a written one. So when the chance came, they decided to try to warp and mash the written Chinese language into use for writing Japanese. The language has evolved over the years to include its own phonetic alphabets (derived from Chinese characters, greatly simplified), but Kanji (lit: Chinese Characters) remains a major part of the Japanese writing system, because they're a lot less ambiguous than writing everything in hiragana or katakana - Japanese contains a lot of homonyms!

Now, there are over 2000 kanji in the set officially recognized by the Japanese government. (If you think that's bad, there are over 12000 in the "Simplified" Chinese set, and something to the tune of 18000 in the "Traditional" Chinese set!) How would we sort, categorize, and recognize them in some sort of sane order? One way to do it is to use radicals. Radicals are commonly recurring components of many kanji, and they a) allow us to sort the kanji set in a logical order and b) sometimes give hints about what the kanji actually MEANS. It's also a lot easier to remember a kanji as a composite of radicals and some extra strokes, as opposed to trying to memorize every single stroke individually for every kanji!

Radicals can generally be classified into several groups. The teacher in the episode talks about hen radicals (which are written vertically, and occupy the left side of the character. It's easiest to use some examples here: 伝, 作, and 体 all have the same hen radical) and tsukuri radicals (also vertical, but occupy the right side - e.g. 顔, 頭).

Most radicals carry meanings on their own. In the episode, the teacher introduces the ninben (see: 伝 (to tell), 作 (to create), and 体 (body)) - which means "person", sanzui (see: 河 (river), 海 (ocean), 流 (to move/flow)) - which means "water", and kihen (see: 村 (village), 林 (forest)) - which means "wood". This is because these radicals are derived from the individual kanji with those meanings. (e.g. ninben is derived from 人, and kihen is derived from 木).

In any case, like this you can compose kanji by combining different radicals - which is incidentally what the teacher tells the students to do in the episode.