Usages
As stated above, katakana characters are mostly used for calling attention to native
Japanese words, for foreign words, and for loan words considered part of the Japanese
vocabulary. For example:
English: Oh no (lit. “It’s terrible!”)! Mary’s glass of milk broke! Romaji:
Taihen da! Merii no miruku no garasu ga kowaremashita! Kana: タイヘンだ！メリーのミルクのガラスがこわれました！
In this example, “ga” は is the particle that indicates the topic of the sentence.
The particle “no” の and the verbs “da” だ (the informal form of
“desu” です, the conjugated form of “to be”) and “kowareru” こわれる are in hiragana
because they’re native Japanese words that don’t have kanji forms. They’re also
not being highlighted here.
“Taihen” is a native Japanese word, usually written in kanji (大変) or hiragana (たいけん).
However, since someone is screaming out, “oh no!”, “taihen” is written タイヘン in katakana
to highlight or bold the word.
“Mary” is a foreign name, so it’s written in katakana: メリー. To write “Mary” in any
other Japanese script would be incorrect, although some foreigners may choose to
do so for artistic reasons.
“Miruku” ミルク and “garasu” ガラス are foreign loan words (originally from the English
“milk” and “glass”) that are considered part of the Japanese language. However,
to indicate their foreign roots, they’re written in katakana. There are very few
exceptions to this rule. However, “coffee” is one of them. It can be written either
in katakana: “koohii” コーヒー or in kanji “kouhii”: 珈琲.
Conclusion
Once you know katakana (after mastering hiragana), you’ll be able to comfortably
read basic Japanese texts, even if you don’t understand them. What does “read and
not understand” mean? For example, even if you don’t know what this English word
means—“zeugma”—because you know how to read English Roman character script, you
can at least guess how to pronounce the word. Japanese is even easier than in English
in that respect; you’ll know how to pronounce a word, not just be able to guess!
Don’t be overwhelmed by all of the special rules (many not even mentioned here!)
for putting foreign words into katakana. If you have a thorough understanding of
the 104 basic combinations and the eight special rules discussed here, you’ll be
able to navigate through new katakana rules you come across with relative ease.
Like with hiragana, the only way to learn katakana is through rote memorization.
So get to it! This website offers flashcards and quizzes to help you this necessary
process.