The rules of kanji reading


I don't completely understand how to read kanji. For example why is in 日立, 日
read as 'hi'? I know the kundoku version is used with okurigana and if kanji
stands alone. Why isn't it used as ondoku reading in the example, which you
are supposed to read with when having multiple kanji together.




You have to consult the dictionary for each word and memorize the
pronunciation.  
There are some general rules but with so many exceptions that they are not
practical.

