結構撐不住
這一支最靠近那個畫面本身：真的有一棟東西在那裡，而它的骨架壞了。
adjective · C1
A building, bridge or other structure that is unsound is in bad condition, because the parts that hold its weight are damaged or weak, so it may not be safe to use.
結構不牢固的
核心畫面
One way to hold this word: a thing still has its shape, but nothing inside it is holding the weight any more. The wall stands, yet the joints have . The plan is still written out, yet the evidence under it is gone. The person is still going about the day, yet the body or the mind is not carrying them. Unsound names that gap between the shape you can see and the strength that should be inside it.
可以想成這樣一個畫面：東西的形狀還在，可是裡面已經沒有東西在撐了。牆還立著，磚縫卻鬆了。計畫還寫在紙上，底下的根據卻…更多收起
可以想成這樣一個畫面：東西的形狀還在，可是裡面已經沒有東西在撐了。牆還立著，磚縫卻鬆了。計畫還寫在紙上，底下的根據卻空了。人照樣過日子，身體或心智卻撐不住了。unsound 指的就是「看得到形狀，撐不住重量」這個落差。所以它幾乎都出現在有人要做判斷的時候：能不能再用、能不能算數、能不能上場。From the word’s history
The source gives the word's make-up directly: un- + sound. Sound on its own is the old word for whole, firm and healthy, and un- takes that away, which is why one word can cover walls, arguments and bodies.
來源直接給了組成：un- 加上 sound。sound 這個字本身的意思是「完好、結實、健康」，un- 把它拿掉。所以同一個字才能同時講牆、講說法、也講身體——被拿掉的都是那個「完好」。
Wiktionary (kaikki extract, source_ref kaikki:3f6f69a190036ae4:672177704:7522): "From un- + sound."
Three branches
說法撐不住
把同一個畫面搬到想法上：結論就像那面牆，底下的證據和推論就是樑柱。
adjective · C1
An unsound idea, argument, method or plan is not built on facts or good reasons, so what it tells you cannot be trusted.
站不住腳的；不可靠的
身體撐不住
再把畫面搬到活的東西上：人或馬看起來還在動，撐著他們的身體或心智卻不完好了。
adjective · C2
Not well in body or mind. This is a formal word, and it appears most often in the phrase of unsound mind, used in law about a person who is not mentally well enough for a decision they made to count.
身心不健全的（正式）