Conjunction し and particle も

Question

I've got a big question about し and も.

1. カロリーも少なくなるし、おなかも張ります。

   Can we not use も here? Will the meaning be changed?

   カロリーが少なくなるし、おなかが張ります。

2. Why does し usually go with も? Does も add some additional meaning? Can we not use も in the example below?

   でも音楽に詳しい友人がいないし、自分もあんまり詳しくありません。

3. Can we say that the part after し is more important than the first part because of も?　

   私の韓国人の俳優のお友達は、矯正をして最高にきれいになりましたし、ぺヨンジュンもデビュー当時はちょっと八重歯風のがありましたが、今は完璧ですよね。

4. Usually も is in the second part or both parts. Why is も used only in the first part of the following sentences?

   • 動物園の夜のナイトサファリのツアーも人気ありますし、電車はMRT(地下鉄)がありますね。
   • DVDは頭だしも速いし、画質がキレイです。

5. Do you have the rule, explaining when we should use も with し？

Thank you!

Answer 1

• Basically you should use either "～が～し～も～" or "～も～し～も～". The first も is optional and it does not significantly change the nuance of the sentence.
• "～も～し～が～" (like your DVD/safari examples) is not wrong, but feels more or less clumsy. IMHO it's always better to say "ツアーも人気だしMRTもある" and "頭出しも速いし画質もキレイ".
• Use at least one も. Otherwise, the sentence will lose the meaning of 'also'.
• This pattern is used to list two (or more) facts of equal importance. Neither the first part nor the second part is more important than the other. Usually the two parts can be safely swapped without changing the meaning.