Learn English – “Could you please” vs “Could you kindly”

In general, the "see you ..." variants mean that you plan to meet the person you are talking to again, whereas the "bye" variants tend to imply that you don't plan to see the person again any time soon. So "see you ..." is often appropriate around family, friends, or the office, because you would normally see the other person again soon on some predictable schedule. "Bye ..." variants may be more appropriate when seeing someone off to a journey or in a shop to the cashier that you don't know. A colleague saying "bye" around the office might mean that he is going on vacation or is changing jobs. (The origin of "goodbye" is "God be with you", so arguably the other person ought to be going on a significant journey that you have to wish such support.)

This distinction is probably lost on many people, but I have seen people startled when the wrong variant is used.

As for the "bye" variants, I'd say

• "goodbye": quite formal
• "bye": casual, sometimes nearly meaningless
• "bye bye": more familiar, sometimes sarcastic

As always, however, it also depends on context and taste.

Actually, sentences that begin with 'could', 'should', or 'would' are questions and should have a trailing question mark. Your original quote, "Could you please pass me the pepper shaker?", could be answered with a "yes" or "no." Although we usually use this syntax as a command it is not the same as the command "Pass me the pepper shaker," or "Please pass me the pepper shaker."

Etiquette tells us that it is more polite to ask for a response than it is to command a response.