英语句式等(理解The word is but a little place,after all.)

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英语句式等(理解The word is but a little place,after all.)
The word is but a little place,after all.这句的意思是"天涯远咫尺,此处又逢君".我想问,but为什么会可以跟在BE动词后面,这是有一种专门的句式吗?还是特殊的什么.我不太懂.

but 这里最好理解成just,或者only,意思是“仅仅”.
例如:
There is nothing but a broken chair in the room.
=There is an only broken chair in the room.