Ok so I’m really struggling with the readings of these two bad boys. There just seems to be no rhyme or reason??
For 月, so far I have learnt つき、がつ and げつ。
For 日, so far I have learnt にち、じつ、か and ひ。
I actually surprisingly do get the difference between on’yomi and kun’yomi (I think ha) so I generally get when the reading should be like, にち as opposed to ひ、 but I think it’s the readings for ‘day’ and ‘month’ that throw me off!!
When/why do I use がつ as opposed to げつ？ I know about month names, both otherwise…??
When/why do I use にち、じつ、か? Is か only for numbered days??
One rule people have shared that has helped me with these two is that it’s generally がつ when taking about a specific month and げつ when talking about months more broadly.
It seems that perhaps a similar thing might superficially apply to じつ・にち.
I pulled the vocabulary on WK that uses either reading and noticed some (albeit tenuous) trends.
Trend 1–にち meaning Japan/Sun
日没 （にちぼつ） sunset
日欧 （にちおう） Japan and Europe
日光 （にっこう） sunlight
日韓 （にっかん） Japan and Korea
日経 （にっけい） Japanese descent
日光浴（にっこうよく）sunbathe
日曜日（にちようび） Sunday
駐日 （ちゅうにち） resident in Japan
Trend 2–じつ being describing types of days and talking about specific-ish time periods
先日（せんじつ） the other day
同日（どうじつ） same day
平日（へいじつ） weekdays
祭日（さいじつ） national holiday
翌日（よくじつ） the next day
祝日（しゅくじつ）holiday
即日（そくじつ） same day
両日（りょうじつ）both days
連日（れんじつ） every day
聖日（せいじつ） holy day
嘉日（かじつ） auspicious day
休日（きゅうじつ）holiday
近日（きんじつ） soon
Trend 3–じつ is usually, if not always, a suffix*
see above
Trend 4–にち describing days generally or describing things that happen on or during days
日程 （にってい） schedule
日記 （にっき） diary
日常 （にちじょう） everyday life
日刊 （にっかん） daily edition
毎日 （まいにち） every day
何日 （なんにち） which day
一日 （いちにち） one day
* I can't say this for certain because I don't know if じつ is only ever used as a suffix.
This is really helpful. The other thing is that some start “sounding right” when you say them (which isn’t that helpful when you are learning them but it does help with recall).
