Uchi-soto in the Japanese language is the distinction between in-groups (uchi, 内, "inside") and out-groups (soto, 外, "outside"). This distinction between groups is not merely a fundamental part of Japanese social custom, but is also directly reflected in the Japanese language itself.

The basic concept revolves around dividing people into in-groups and out-groups. When speaking with someone from an out-group, the out-group must be honored, and the in-group humbled. This is achieved with special features of the Japanese language, which conjugates verbs based on both tense and politeness. It may also include social concepts such as gift giving or serving. The uchi-soto relationship can lead to someone making great personal sacrifices to honor a visitor or other person in an out-group.

One of the complexities of the uchi-soto relationship lies in the fact that groups are not static; they may overlap and change over time and according to situation.

Uchi-soto groups may be conceptualized as a series of overlapping circles. One's position within the group, and relative to other groups, depends on the context, situation, and time of life. For example, a person usually has a family, a job, and other groups or organizations they belong to. Their position within the various groups, and in relation to other groups, changes according to circumstances at a given moment.

Thus, a company employee may occupy a superior position within the specific company, but a humble one in relation to the company's customers. The same employee may hold a black belt, giving them a superior position within a karate club, but they may be a beginner at tennis and thus occupy an inferior position in the tennis club.

The workplace is a typical example: the employees below a middle manager are in his in-group, and may be spoken to using casual speech, while his bosses, or even, in large companies, people in other departments, are in an out-group, and must be spoken to politely. However, when dealing with someone from another company, one's own entire company is the in-group, and the other company the out-group. Thus, it is acceptable for the middle manager to speak of his own company, even the bosses, in non-honorific speech. This emphasizes that the company is one group, and although that group may have subdivisions inside of itself, it does not include the other company.

For example, when speaking with subordinates a manager might omit the honorific -san, whereas he would be unlikely to do so when addressing his superiors. On the other hand, when dealing with an outsider—essentially any person not directly connected to the company—he omits all honorifics when speaking about anyone in the company, including his superiors.

However, if the same manager speaks to a subordinate about his family, he refers to the subordinate's family, which is the subordinate's in-group but not his, in polite terms, but his own family, which is his in-group but not the subordinate's, in plain language. Thus, the manager and the subordinate both refer to their own families as kazoku (family) and to the other's family as go-kazoku (honorable family).

In addition to features of the Japanese language, uchi-soto also extends to social actions. For instance, in a Japanese home the most senior family member, usually the father or grandfather, normally takes a bath first; the rest of the family follows in order of seniority. A visitor to the home, however, is offered the first bath. Similarly, an overnight guest is offered the best sleeping arrangements, even if this greatly inconveniences the rest of the family. This latter case is a difficult point for Westerners in Japan, who are usually taught to be polite by refusing accommodations that inconvenience others.

Read more about Uchi-soto:  Foreigners in Relation To The Uchi-Soto System, Language Examples

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