Hiragana vs Katakana — when do Japanese people actually use which?

sarah_j

I have been studying kana for a few weeks now and I understand the textbook explanation: hiragana is for native Japanese words and grammatical elements, katakana is for foreign loanwords. Fine. But when I look at actual Japanese text — menus, signs, manga, social media — the usage seems much more nuanced than that.

For example:

I see katakana used for Japanese-origin words sometimes (not loanwords)
Onomatopoeia seems to appear in both scripts depending on the context
Some words appear to be written in katakana for stylistic or emphasis reasons
Scientific and medical terminology often uses katakana even for non-foreign concepts

My questions:

When do Japanese people choose katakana for non-loanword contexts?
Is there a rule for onomatopoeia, or is it purely stylistic?
How do native speakers think about this choice — is it instinctive, or are there genuine rules?

I am studying at NYU and my professor gave a somewhat simplified answer that left me wanting more. I feel like there is a deeper layer here that the standard beginner materials skip over. Any native speakers or advanced learners here who can shed light on this?

osakadreams

Living in Osaka, I see this daily. Katakana shows up everywhere beyond just loanwords. Menus use it to make food sound premium — コーヒー hits different than 珈琲 or こーひー. Also used for animal/plant names in scientific contexts, and yes, for stylistic emphasis — like using italics in English. In manga especially, katakana on a word that would normally be hiragana signals a foreign accent, a robotic voice, or just extra weight. It's absolutely instinctive for natives but it maps to real patterns once you start noticing them.

Marta

Desde una perspectiva más lingüística: la clave está en que el katakana funciona como marcador de otredad o distancia semántica. Las onomatopeyas en japonés (擬音語 y 擬態語) aparecen en ambos sistemas, sí, pero el katakana les da una textura más dura, más impactante — ドン suena más brutal que どん, habéis de reconocerlo. No es una regla fija, es una convención estilística muy arraigada. Para el N5 no os preocupéis demasiado por esto, pero para leer manga o literatura real, os interesa mucho internalizarlo.