Confused about the usage of tense in this sentence...

Hello everyone!

I'd like to ask for some help in understanding the use of kaetta vs. kaerimasu in this sentence from module 5.3.

You should return home for Christmas:
クリスマスに帰ったほうがいいですよ / ​Kurisumasu ni kaetta hō ga īdesu yo

Why isn't it:
クリスマス に 帰ります ほう が いい です よ / kurisumasu ni kaerimasu hō ga īdesu yo

I read kaetta as "went back / returned" - but the sentence isn't in the past tense.  It seems to me it says "you should have returned for Christmas" rather than a recommendation to what to do moving forward.  I'm assuming it's because nothing should come after the ~masu tense in the sentence, so the tense needed to be changed to allow for hō ga īdesu yo.  But I'm not sure, and if so, then why the past tense?

Thank you very much for any light you can shed!! :-)

Hi イリニ、correct, this has to do with only the main verb getting conjugated (for polite form), and also that the formation of noun phrase that is being "sided with" uses short form:

Ex: The noun phrase "the sweater I bought" is "bought sweater" in Japanese noun phrase structure:  買った　(かった)　セーター　

So, the sweater I bought is too small becomes: 買った　セーターは　小さすぎます。

The sentence structure in the module is something like:

(A/The) "Christmas home return" side/way is good.

ほう (方) - direction, side, way

[A] ほうが 　〜[B]より is the grammar structure for comparing A to B's quality, and without the より, it has the "this way is better/preferred/suggested" implication.

In Genki I, this 〜ほうがいいです structure is covered in 12.3 (page 272). It's a little quirky in that it's in short form past for positive advice and short form present in negative "not to do" advice.

こんにちは (Konnichiwa) イ リ ニ and toru e,

Thanks for the question! 

toru e, you're spot on! The reason かえった (kaetta) is in the past tense in this sentence is because this is the conjugation for ほう　が　いい (hō ga ī). ほう　が　いい (Hō ga ī) is used with verbs in the past plain form to talk about suggestions and say you "should" do something, or it's "better to" do something. 

When we use ほう が いい (hō ga ī), the overall tense is determined by the END of the sentence. Since いい (ī) is in the present tense, we know that this is talking about a future suggestion: not a past suggestion. 

If we were talking about a past suggestion, we would say:

クリスマス　に　かえった　ほう　が　よかった　です　よ 。 (Kurisumasu ni kaetta hō ga yokatta desu yo) "(You) should have returned home for Christmas."

Don't worry about the tense of the verb before ほう が いい (hō ga ī). This will always be in the past since this is the conjugation pattern.

I highly recommend checking out this new lesson to get a better idea of how to use ほう が いい (hō ga ī).
https://members.rocketlanguages.com/members/japanese/lessons/5173/6-6-Using-the-Past-Plain-Form

I hope this helped! Please let me know if you have any other questions!

べんきょう　を　がんばって　ください！ (Benkyō o ganbatte kudasai!)