It’s a question I sometimes get asked not only by beginners, but also by advanced students.The answer is simple, but I’ll write it out to make sure you understand it.
“Arigato” expresses gratitude. You say it when someone has done something for you—for example, if your boss helped you with something at work.
“Tetsudatte kudasatte, arigato gozaimashita.” (1)The past tense “gozaimashita” is used because your boss had already helped you before you said it. This makes sense, doesn't it?
However, the present tense “arigato gozaimasu” can also be used in this case. That’s why these expressions cause confusion.
Consider this next example. Let’s say your client is going to prepare some documents for you by next week.
“Arigato gozaimasu. Yoroshiku onegai shimasu.” (2)The present tense is used because your client hasn’t prepared them yet. In this case, you can’t use the past tense. Remember: The past tense can’t be applied to incomplete events. This is a rule!
Let’s have a look at other expressions: “Otsukaresama desu” and “otsukaresama deshita.”The same rule applies here, too.
It’s 7 PM and all employees are going home after work. What would you say to your colleagues?
“Otsukaresama deshita.” (1)Work for the day is finished (1), so the past tense “deshita” is used. Japanese people say this to each other to mutually acknowledge their hard work. Like “arigato”, you can say “otsukaresama desu” in the present tense.
Actually, you always hear “otsukaresama” at Japanese companies during the day and not only at the end of the day or after long meetings. People say it whenever they pass by each other. You can consider this expression to be a greeting used in the same way as “ohayo” and “konnichiwa.”
And, in cases where work is not over yet (2), you should say it like this:
“Otsukaresama desu.” (2)Even in the middle of the day, it expresses something like “You’ve been working hard today. Are you tired? Are you okay?”
Moving on, how about these expressions: “Osewa ni narimasu” and “osewa ni narimashita”? It’s not easy to translate them into English, but do you understand their meaning?
They are used when expressing gratitude to someone for taking care of you, helping you, or working with you.
For example, when you leave a company where you’ve worked for five years, you feel grateful to your colleagues.
"Ima made taihen osewa ni narimashita." (1) (Thank you very much for all of your kind help.)The act of receiving help from your colleagues has finished, so in this case, the present/future tense is not used.
On the other hand, when you begin working at new office, you expect that your new colleagues will work with you and help you a lot. So, you say,
"Korekara osewa ni narimasu." (2)This is about future, therefore “narimasu” is used and only this form is possible.
What would you say to clients you have been working with for a while?
Itsumo osewa ni natteimasu. (3)
Itsumo osewa ni natteorimasu. (polite version)“Teimasu”, indicating a ongoing state, is used because these refer to a daily situation. When you want to be polite, convert “imasu” to its humble form, “orimasu.”
These are very typical Japanese greetings and essential at Japanese offices. I hope you can use these expressions correctly in various situations.