There are rules, though they are far from perfect and don't cover every case. The readings you're having trouble with have to do with the two kinds of on-readings: 漢音 and 呉音. For example, someone in this thread on this forum posted a rough rule about the readings of 人 originally posed on 2ch. It can predict the readings of words of the form XX人 with good accuracy. Technically the rough rule posted on this forum is describing how 漢音 and 呉音 of the kanji 人 behave and how they're related to the meaning and grammatical function of XX in XX人.
I know a longer explanation based on etymology and such can be opaque and even mysterious to some people. But you might find this simple rule helpful:
XX人 is XXじん if XX is describing an action and 人 is "the person who gets XXed" e.g., 殺 (to kill) is a kanji describing an action. And 人 in 殺人 (murder/killing) is the person/people who are killed. So it's さつじん.
XX人 is XXにん if XX is describing an action and 人 is "the person who does XX" e.g., 犯人 means "a criminal," i.e., a person who committed a crime. So, unlike 殺人, the part 人 is the person who does/did the action. So it's はんにん.
If you pronounce 殺人 as さつにん when talking about a serious crime, as the above second rule suggests, it can sound like a newly coined word which means "murderer" if it fits in context;
漢音 of 人 (じん)= person who is XX'ed,
呉音 of 人 (にん)= person who does XX.
I'm not saying さつにん would be treated as an accepted word though.
There are rules for when XX is not an action too. If you're interested, the linked thread has a little more. This isn't particularly esoteric knowledge. This is more like a grammar rule than a random reading phenomenon because you can coin a word on the fly using the knowledge. So I think you can find more detailed explanations somewhere else maybe in English too.
I have also read about how the readings of 人 and certain grammar rules in Spanish behave similarly somewhere on the internet. But I don't speak Spanish and forgot where it was.
As for the readings of 大, some cases are quite simple and regular if you have knowledge of 漢音 and 呉音.
大 in a word of the form 大XX (XX can be a single kanji) is generally read as:
だい if XX is a word of Chinese origin with a 呉音 on-reading,
たい if XX is a word of Chinese origin with a 漢音 on-reading,
おお if XX is read with its kun-reading.
There are exceptions. Some words allow multiple readings. I don't think your average beginner textbook teaches 漢音, 呉音, and their behaviors in detail. I wouldn't recommend you learn this kind of thing either; it's definitely overkill. But it might be helpful to know the fact that there are rules which can predict the readings in certain cases fairly accurately.
I know a longer explanation based on etymology and such can be opaque and even mysterious to some people. But you might find this simple rule helpful:
XX人 is XXじん if XX is describing an action and 人 is "the person who gets XXed" e.g., 殺 (to kill) is a kanji describing an action. And 人 in 殺人 (murder/killing) is the person/people who are killed. So it's さつじん.
XX人 is XXにん if XX is describing an action and 人 is "the person who does XX" e.g., 犯人 means "a criminal," i.e., a person who committed a crime. So, unlike 殺人, the part 人 is the person who does/did the action. So it's はんにん.
If you pronounce 殺人 as さつにん when talking about a serious crime, as the above second rule suggests, it can sound like a newly coined word which means "murderer" if it fits in context;
漢音 of 人 (じん)= person who is XX'ed,
呉音 of 人 (にん)= person who does XX.
I'm not saying さつにん would be treated as an accepted word though.
There are rules for when XX is not an action too. If you're interested, the linked thread has a little more. This isn't particularly esoteric knowledge. This is more like a grammar rule than a random reading phenomenon because you can coin a word on the fly using the knowledge. So I think you can find more detailed explanations somewhere else maybe in English too.
I have also read about how the readings of 人 and certain grammar rules in Spanish behave similarly somewhere on the internet. But I don't speak Spanish and forgot where it was.
As for the readings of 大, some cases are quite simple and regular if you have knowledge of 漢音 and 呉音.
大 in a word of the form 大XX (XX can be a single kanji) is generally read as:
だい if XX is a word of Chinese origin with a 呉音 on-reading,
たい if XX is a word of Chinese origin with a 漢音 on-reading,
おお if XX is read with its kun-reading.
There are exceptions. Some words allow multiple readings. I don't think your average beginner textbook teaches 漢音, 呉音, and their behaviors in detail. I wouldn't recommend you learn this kind of thing either; it's definitely overkill. But it might be helpful to know the fact that there are rules which can predict the readings in certain cases fairly accurately.
Edited: 2010-12-15, 4:05 pm
