Meaning of the phase: 筋ってもんだ


I'm having a bit of trouble getting a grasp of 筋ってもん (sujitte mon) and what
it's supposed to convey. Does it possibly have kind of declarative function
for whatever precedes it?

Examples include:

> 俺の通すべき[筋]{すじ}ってもんだ

and

> 生身でもがくのが筋ってもんだ

Any help is appreciated.




I suspect the core of your confusion comes from not knowing a meaning of 筋{すじ}
which is applicable in both of your sentences; that is:

> ❺ 物事の論理的な流れ。道理。  
>  「➖の通った話」  
>  明鏡国語辞典 第二版

This usage of 筋 is pretty idiomatic and mostly found in the expressions 筋が通る
or 筋を通す, which you should be able to look up directly.

「〜するのが筋だ」 stems from that usage and basically means that 〜 is the reasonable,
logical, right, or natural thing to do.

The ってもんだ is best explained in detail elsewhere (see [this
answer](https://japanese.stackexchange.com/questions/28872/how-to-
parse-%E8%A6%AA%E3%82%82%E8%BE%9E%E6%9B%B8%E3%82%92%E8%B2%B7%E3%81%A3%E3%81%A6%E3%82%84%E3%81%A3%E3%81%9F%E3%81%8B%E3%81%84%E3%81%8C%E3%81%82%E3%82%8B%E3%81%A3%E3%81%A6%E3%82%82%E3%82%93%E3%81%A0/29018#29018),
h/t Chocolate for finding that), but it’s basically a masculine-ish way of
giving a “that’s the way things are” sort of finality to your sentence.
Overall, I would say that 筋ってもんだ is not so common a collocation to be able to
treat it as a single unit, so it is likely better to consider them separately.




I suspect the core of your confusion comes from not knowing a meaning of 筋{すじ}
which is applicable in both of your sentences; that is:

> ❺ 物事の論理的な流れ。道理。  
>  「➖の通った話」  
>  明鏡国語辞典 第二版

This usage of 筋 is pretty idiomatic and mostly found in the expressions 筋が通る
or 筋を通す, which you should be able to look up directly.

「〜するのが筋だ」 stems from that usage and basically means that 〜 is the reasonable,
logical, right, or natural thing to do.

The ってもんだ is best explained in detail elsewhere (see [this
answer](https://japanese.stackexchange.com/questions/28872/how-to-
parse-%E8%A6%AA%E3%82%82%E8%BE%9E%E6%9B%B8%E3%82%92%E8%B2%B7%E3%81%A3%E3%81%A6%E3%82%84%E3%81%A3%E3%81%9F%E3%81%8B%E3%81%84%E3%81%8C%E3%81%82%E3%82%8B%E3%81%A3%E3%81%A6%E3%82%82%E3%82%93%E3%81%A0/29018#29018),
h/t Chocolate for finding that), but it’s basically a masculine-ish way of
giving a “that’s the way things are” sort of finality to your sentence.
Overall, I would say that 筋ってもんだ is not so common a collocation to be able to
treat it as a single unit, so it is likely better to consider them separately.

