Pronunciation of 年


The general rule to choose between _kun_ (とし) and _on_ (ネン) readings does not
seem to work here. Are 今年, 去年, 来年, 毎年, 半年, etc. different kinds of compounds
justifying using different readings? Is this the usual rule applied in a
subtle or complicated way?




I think it might be much more helpful for you to think of "words" having
"writings" rather than "characters" having "readings".

For instance, as a speaker or learner or Japanese you know the "word"
きょう(today) and you know the "word" あした(tomorrow). Then, you learn how to
"write" or "spell" these words:

> **今日{きょう}、明日{あした}**

Then, maybe later you pick up the word あす( _also meaning tomorrow_ ) and you
ask, how do I write that? And the teacher/your mom/おばあちゃん etc. says "It's
written the same way as あした". You think, "Oh, OK"... and you go about your
business.

Then, you are taught how to write the word you know for yesterday（昨日{きのう}）and
you also learn how to write the days of the week like,
日曜日{にちようび}、月曜日{げつようび}、火曜日{かようび}、etc.

At some point you take a class trip to 日光{にっこう} and you have such a great time
that you want to write a letter to your おばあちゃん to tell her all about it.

Maybe you write something like this in your letter,

> 昨 **日** 、遠足{えんそく}で **日** 光に行{い}ってきました。すごく楽{たの}しかったです！ **日** 曜 **日**
> に帰{かえ}りました。明 **日** はおばあちゃんのとこに行きます。写真{しゃしん}をおばあちゃんに見{み}せたいです。

  * _Yesterday, (we) went on a field trip to Nikko. It was a lot of fun! (We) came back on Sunday. (We) are coming to your house tomorrow. I want to show you the photos (I took in Nikko)._

As you were writing your letter, you didn't think about whether the
character「日」is read のう、にっ、にち、び、す、した and neither did your おばあちゃん as she was
reading it.

The point of the story is that thinking of characters as having readings is
often a bit like putting the cart before the horse. Most of the time,
especially in the beginning, you will already be familiar with a word _and
then_ you will learn how to write/spell/read it.

Later on, when you come across a word only in writing that you do not know you
will likely know how to look it up and learn the pronunciation and meaning
together (though you could probably guess from your experience with other
words and characters).

Just to reiterate, it is much more helpful to think of **_words that have
writings_** , rather than _characters that have readings_. All the more so for
very common words.

To directly answer your question, there is no subtle rule in these cases as to
how a word will be written, even some on-yomi are usually written in kana. （
**さっそく** 、 **がん** 、そろ **ばん** 、 **ぜんぜん** ）

  1. First you learn a word 
  2. Then you learn how it can be written
  3. Then you encounter it in the world and decide how to read it

If there is any general rule to comment on, I think it would just be that on-
yomi tend to be more formal or academic, whereas kun-yomi tend to be more
frank or poetic. So if you have a choice, like in the case of,

  * 毎年{まいねん}(on-yomi + on-yomi) 
  * 毎年{まいとし}(on-yomi + kun-yomi)

...you would probably want to read まいねん if the context is formal, and まいとし if
it is not formal.

  * ことし、こんねん → **今年**

  * まいとし、まいねん → **毎年**

