Which day is the beginning of the week, Sunday or Monday?
The Gregorian calendar, currently used in most countries, is derived from the Hebrew calendar, where Sunday is considered the beginning of the week. Although in Judaism the Sabbath is on Saturday, while in Christianity it is on Sunday, Sunday is considered the beginning of the week in both religious traditions. Because Sunday is the beginning of the week culturally and historically, many calendars follow this rule.
Currently, a five-day workweek has been well-established worldwide and most people consider Saturday and Sunday to be the weekend. In that case, it is more practical to consider Monday, the end of the break and the start of work, as the beginning of the week.
In fact, in 1971, rules were established that Monday was considered the beginning of the week in daily life and business practices, recommended by the ISO (International Organization for Standardization). Accordingly, Monday through Sunday are indicated by numbers, 1 to 7.
A new method of specifying the date by week number and day number has been utilized since then, which is why some European calendars regard Monday as the beginning of the week.
There is no wrong answer in this debate. However, it is important to be aware that if you say, "Sunday this week" or "Sunday next week" in the office or at home, the other party might have a different opinion.