grammar - Can you use the polite form ます with ので?

I was recently told by someone that you cannot use the polite form ～ます and ので; that is, ので must be used with the plain form. (Specifically, he was saying that 「勉強していますので」 was wrong, and had to be changed to 「勉強しているので」.)

That sounded a bit dubious to me when I heard it, since I've seen plenty of sentences which involve ～ます verb and ので. So I went and checked online a bit. The majority of results I found were perfectly okay with using ～ますので, but a couple seemed a bit strange.

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  This page downright says "don’t use –masu at the end of the verb", but doesn't explain why.

  
  


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  I wasn't able to fully read this entry, but it seemed to talk about what I'm asking. Could someone just give a brief summary of what it talks about?

  
  
  

So was the person who told me you can't use ～ますので mistaken, or is there some deeper commotion about this that I'm not aware of?

Answer

To answer the title question, I would have to say, "Yes, you can."

If you lived in Japan, you would hear 「ますので」 at least a few times everyday and even more times on some days. We use it whenever we speak rather politely. When do we speak politely? We do so in business, in conversations with teacher/mentor figures, strangers, etc. 「ますので」 is needed because it sounds better than 「ますから」. 「から」, at times, sounds too light and informal to go with 「ます」 and using 「ますので」could solve this problem instantly.

Foreign language learners, however, when they learn that two words have the same meaning, naturally tend to switch them around too freely in what they say or write. They use the two words (in this case, 「から」 and 「ので」) interchangeably without making necessary alterations in the other parts of their speech or writing. This is the reason that 「ますので」 could sound "off" if not incorrect at times if you forget to make everything else on the same politeness level as 「ますので」. This is also what your second link talks about as well. (Forget about your first link as its author clearly does not know enough Japanese.)

「[勉強]{べんきょう}してるから、[電話]{でんわ}しないでね。」 Natural and informal. Just nice.

「勉強してるので、電話しないでね。」 Borderline natural as 「ので」 is a bit too heavy to go with the informal second half.

「勉強していますので、電話しないでね。」 Grammatical but very unnatural.　Polite top and informal bottom.

「勉強していますので、電話はしないようにしていただけますか。」 Natural combo of first and second halves.