Plain form/polite form verbs

Hi there,

I'm a bit confused with how to use plain/polite verbs in Japanese. In the Genki Book there are examples where the main clause has the ~masu stem verb and the subordinate clause has a plain/simple dictionary form.
Maybe I feel so confused because English has strict rules for the sentences (e.g. in complex sentences all clauses have to be in the same tense = sequence of tenses). I would expect Japanese also has such rules where both main and subordinate clause have to be either polite or plain, but not both at the same time. Anyway, here are the examples:

1. 今日は病気だから，運動しません (今日は病気ですから，運動しません/ 今日は病気だから，運動しない???)
2. 雨が降っているから、散歩しません (雨が降っていますから、散歩しません/ 雨が降っているから、散歩しない???)
3. 友だちがいなかったから、すごくさびしかったです (友だちがいませんでしたから、すごくさびしかったです/ 友だちがいなかったから、すごくさびしかった???)

You typically only use です or ～ます (teineigo) once in a sentence, at the end. It's redundant to use it again in the middle. Sometimes you do it, but not as a general rule.

What you're guilty of here is called a hypercorrection, where you assume there is a rule that doesn't exist and then "correct" for that rule. The result of hypercorrection is often wrong. If you haven't been told that there is a rule to do something, don't assume that it is there.

TL;DR: The examples that GENKI gives are correct. Follow them. If something in there looks off to you, what needs to change is your understanding of Japanese grammar.

JuliMaruchan said:

You typically only use です or ～ます (teineigo) once in a sentence, at the end. It's redundant to use it again in the middle. Sometimes you do it, but not as a general rule.

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Thanks, that's an explanation I've been looking for in Genki. It might be natural and self-explanatory to you, but I really need an explanation why it is like this for every little thing So, thanks!

Actually, it differs depending on the conjunctive particle.
You can also use the polite form before から, so there is no problem with 病気ですから or 降っていますから in your examples. However, only plane forms are usually used for some other particles, for instance のに, thus, 雨が降っていますのに、散歩します sounds odd (not ungrammatical but almost never used). This is because のに has a strong subordination to the main clause.
On the other hand, you need to unify the level of politeness for が (e.g. 雨が降っていますが、散歩します, not 雨が降っているが、散歩します), since these two clauses are closer to two independent sentences. Speaking strictly, this is more likely a coordinate clause, not a subordinate clause, though.
Incidentally, the tense in Japanese grammar is rather different from the English one. You'll come across it soon.

Thanks Toritoribe, yes I think I've also read somewhere that you should use plain forms before のに. So the tendency is to use plain forms in subordinate clauses and it's possible to use the polite forms if the subordination is rather weak. That's great to know.

I don't really get what you mean about the tenses though. Or better to say, what do tenses have to do with my confusion about the usage of plain/polite form?

Because you mentioned it.

dhmkhkk said:

Maybe I feel so confused because English has strict rules for the sentences (e.g. in complex sentences all clauses have to be in the same tense = sequence of tenses). I would expect Japanese also has such rules where both main and subordinate clause have to be either polite or plain, but not both at the same time.

Click to expand...

There also are rules for the tense in Japanese grammar, which has a different system from the English one. It's strict since the meaning of the sentence, for instance the temporal order of the two events described in each clauses could change by it.
On the other hand, even though the sentence could sound odd, the meaning is never changed by the level of politeness, thus, there is a difference in the required strictness between the tense and politeness level in the first place.