外出 and 外泊: going out and staying overnight
Compare going out to shop with staying overnight at a friend’s house, without inferring a return time or an overnight stay from 外出 alone.
外出 focuses on going out
外出 (がいしゅつ) focuses on leaving home to go out. The surrounding words tell you what the outing is for.
“午後から買い物のため外出した。” says that the speaker went out to shop in the afternoon. 買い物のため gives the purpose, while 外出した states the action of going out.
外泊 focuses on a night away from home
外泊 (がいはく) focuses on spending the night away from home. A stated place tells you where the person stayed.
In “友人の家に泊まり、久しぶりに外泊しました。”, the speaker stayed overnight at a friend’s house for the first time in a while. The place and the overnight stay are both stated.
Check going out and staying overnight separately
The examples compare going out to shop with staying at a friend’s house. The first sentence centers on going out, while the second centers on spending a night away from home.
外出 alone does not tell you what time the person returned or whether they stayed overnight. The 外泊 example describes a stay at a friend’s house; it does not establish a reporting rule.
Does “午後から買い物のため外出した。” alone tell you that the person stayed overnight away from home?
Show the answer and why
No. It states that the person went out to shop, without giving a return time or saying whether they stayed overnight. The separate 外泊 example explicitly describes a night at a friend’s house.