Here is the link to my initial analysis if you want to read:
Katakana Analysis Draft
Thanks to all the great commentary by the higher-level Japanese students, it was greatly appreciated. I will now paraphrase and revise my original analysis.
カタカナ, in the textbook examples is generally defined as used for onomatopoeia, foreign loanwords, and for emphasis. The last category seems to be the most vague and brings confusion even to native Japanese speakers. I originally said that the purpose of this vague category could be attributed to the popularity of writing words in カタカナ to connect to the more trendy 'Western' world and imply a connection to the future, which is why some of the カタカナ words have hiragana and kanji counterparts but カタカナ is used anyway. There is also importance in shape of the カタカナ, that it is seen as more masculine, as contrast to feminine hiragana and the sharpness of the characters that can give different connotations to the words written in that fashion.
I would revise my current description by adding how the switches to カタカナ can act in part, as italics, capitalization, and bold style of writing, and to add nuance to a phrase or word. An interesting point one of my commenters has brought up is, 'what would be the significance of writing someone's name is hiragana?' It is interesting to note how the katakana rules are more vague compared to katakana and I think the alphabets serve to distinguish the Japanese from the non-Japanese, although with the recent trend, it appears that the younger generation wants to make more connections with the Western world. Also, I agree with another commenter that part of the reason that some of the Japanese textbooks do not mention all the nuances and give stricter definitions of カタカナ in order to keep the Japanese student less confused in the beginning, which I sort of implied by remarking that such ambiguity could disillusion prospective learners of Japanese. Another commenter also added to the definition of カタカナ by saying that the use of katakana implicitly expresses sensation, emotion, and feelings that cannot be completely expressed in hiragana.
Sorry for such the long post, but the uses of カタカナ are many and varied, not able to fit in a a single definition or category. Hope you guys gained a better understanding of the many nuances of カタカナ from this post!
