よん or し? (4 or 4?)
I know that there are two ways of saying 4 in Japanese, with yon and shi, but I'm kinda curious if there are rules to when to use one or the other. I already know よん can be used when counting down, but what about counting up. Or times where you are simply saying the number by itself. Thanks if you can answer.
I don't want to scare you away, but most numbers have two main readings with further modifications depending on what you're counting. There is the Chinese reading, and the Japanese reading, and which one to use depends on what you're counting.
4 is kind of a special case within special cases. Which one a Japanese person will use when just straight up listing the numbers will depend on who they are, which direction they are counting, and if you give them time to think beforehand. I encourage trying this with a Japanese friend, ask them to count up and then down, and then ask why they used different words. They probably won't be sure. Both versions of 4 are fine to use when just counting like that.
Now, for quantities it gets more complicated and specific. Most often you're gonna use a reading based on the Japanese よん. The ending will change based on what you're counting:
4.79 - よんてんななきゅう - yon ten nana kyuu
4 o'clock - 四時 - よじ - yoji
4 (general) things - 4つ - よっつ - yottsu
The other reading, し (shi), is often used when talking about dates or in set phrases and words:
April (4th month) - 4月 - しがつ - shi gatsu
The 4 seasons - 四季 - しき - shi ki
Don't even get me started on 7 :P