兼ねる: two uses of one room and two roles of one owner
Identify the guest-room and study functions of the same room, and the owner and chef roles held by the same person.
Two functions or roles attached to one subject
兼ねる (かねる) means to serve as both or combine roles. In these sentences, one room serves as a guest room and a study, and one person holds the roles of restaurant owner and chef.
Identify both functions or roles together with the subject that holds them. Two uses do not make the room two rooms, and the owner's chef role does not introduce a second employee.
The shared room and the owner who is also chef
「この部屋は客間と書斎を兼ねている。」 (This room serves as both a guest room and a study.) この部屋 holds the two functions of 客間 and 書斎. They are uses of the same room; the sentence does not require all activities in it to occur simultaneously.
「店主が料理人を兼ねる小さな食堂だ。」 (It is a small restaurant where the owner also serves as chef.) The small restaurant's owner also serves as its chef. 店主 and 料理人 are two roles of the same person here, rather than two separately identified employees.
Read the combined functions and combined roles
The room sentence concerns functions of a space; the restaurant sentence concerns roles of a person. Identify what serves as what around 兼ねる to retain the shared subject of the two uses.
These examples describe a combined arrangement. They do not require every action to happen at once, and they supply no inability or refusal to perform a task.
Does the owner also serving as chef mean there are two separate people?
Show the answer and why
No. The same restaurant owner also holds the chef role. The two role names belong to one person in this sentence.