Are でしかない and にすぎない synonymous? Or is there some connotation?


For example:

> 事故にあって、あなたが無事なら、心配いらない。車は車でしかないよ。

can be swapped for

> 事故にあって、あなたが無事なら、心配いらない。車は車にすぎない。

without changing the meaning




Yes, 車は車 **でしかない** can be swapped for 車は車 **にすぎない** without changing the
meaning.

In the given context, they have the same meaning as "The car is only a car.",
which implies "The car is only a car unlike your life. No matter how damaged
it gets, it can be compensated by such as repairing it or replacing it with a
new one."

* * *

# EDIT

> ...are there instances where swapping is impossible?

Very few, but certainly there are.  
There is a corpus named "少納言｛しょうなごん｝"
[here](http://www.kotonoha.gr.jp/shonagon/), which collected a vast number of
actual Japanese sentences. In this corpus, I searched for sentence examples
with "でしかない" as a keyword, and I examined whether they can be replaced with
"にすぎない".  
In many cases, I found they could be, but I found an example that couldn't be
replaced with にすぎない, which is shown below.

> だが、自分の老後を頼れるのは朔太郎｛さくたろう｝ **でしかない** と、信じていた。

This sentence could be rewritten as: だが、自分の老後を頼れるのは朔太郎｛さくたろう｝
**を除いて（他｛ほか｝に）いない** と、信じていた。  
_However, I believed that there was no one except Sakutaro whom I could depend
on for the life of my old age._




Yes, 車は車 **でしかない** can be swapped for 車は車 **にすぎない** without changing the
meaning.

In the given context, they have the same meaning as "The car is only a car.",
which implies "The car is only a car unlike your life. No matter how damaged
it gets, it can be compensated by such as repairing it or replacing it with a
new one."

* * *

# EDIT

> ...are there instances where swapping is impossible?

Very few, but certainly there are.  
There is a corpus named "少納言｛しょうなごん｝"
[here](http://www.kotonoha.gr.jp/shonagon/), which collected a vast number of
actual Japanese sentences. In this corpus, I searched for sentence examples
with "でしかない" as a keyword, and I examined whether they can be replaced with
"にすぎない".  
In many cases, I found they could be, but I found an example that couldn't be
replaced with にすぎない, which is shown below.

> だが、自分の老後を頼れるのは朔太郎｛さくたろう｝ **でしかない** と、信じていた。

This sentence could be rewritten as: だが、自分の老後を頼れるのは朔太郎｛さくたろう｝
**を除いて（他｛ほか｝に）いない** と、信じていた。  
_However, I believed that there was no one except Sakutaro whom I could depend
on for the life of my old age._

