How do ことになる and ようになる differ? (When ことになる cannot = "It has been decided that")?

Question

I understand that ことになる has the meaning "It has been decided that" and can be used to point to a ritual or habit of a society like taking off your shoes. However, I don't get what it means when it is like this: あすで１週間雨が降りつづくことになる。 How is that different from say, あすで１週間雨が降りつづくようになる。 Thankyou :)

Answer 1

～ことになっている is for a custom or a decided rule, ～ことになる is something has been decided by someone other than yourself.

あすで１週間雨が降りつづくことになる。In the morning, it will have continually rained for a week. <<the situation has arisen; KOTO is a nominalizer, and it's now THINGになる, "becoming THING">>

>> あすで１週間雨が降りつづくようになる。This doesn't seem right to me. To my knowledge, the ようになる is used to mean "become able to do," usually as a gradual change and the subject is usually an animate being. The embedded clause, if it's affirmative, is USUALLY in the potential.

漢字が読めるようになりました。- I've reached the point where I can read kanji.

漢字を読まないようになりました。- I've reached the point where I can't read kanji. (can no longer read kanji)

漢字が読めるようになりません。- I haven't reached the point where I can read kanji yet. (haven't made it to that point)

As weather is NOT animate, your sentence cannot work.