Hiragana: How does dakuten affect chi and tsu?


In the Human Japanese app, it says that chi and tsu become ji and zu
respectively, while on Wikipedia it says that most commonly, they become shi
and su.




Imagine the dakuten as a mark that transforms unvoiced phonemes (sounds that
make up a language) to voiced phonemes. A quick-and-dirty way to tell whether
a phoneme is voiced is checking whether making that sound makes you use your
vocal cords or not. For example か (ka) is unvoiced, が (ga) is voiced. と (to)
is unvoiced, ど (do) is voiced. You're making the same formation in your mouth
to produce the sound, but the voiced one uses your vocal cords. This should
hold true for EVERY pair of characters with and without dakuten.

So it holds true to adding dakuten to ち (chi) and つ (tsu). The issue arises
because the characters resulting from adding a dakuten to "chi" and "tsu," (ぢ
and づ respectively) are much more difficult to approximate with English
phonemes. Try saying ち or つ while using your vocal cords and you'll get
something like "dji" and "dzu." Much harder to romanize than "ka ki ku ke ko."
While most Japanese phonemes have pretty straightforward English analogues, ぢ
and づ are oddballs, backing up the age-old adage that learning the script of
the language is immensely helpful to capture things that you might not catch
with romanization.

As a side note, words containing づ are not super common (though they do exist,
such as 続く／つづく and 葉月/はづき), and words with ぢ are even rarer.

