Marks the verb after it as impossible for the subject to carry out; sits before a verb to say there is no way to do it.
框 · Frame
[subj] 無法 [verb phrase]
觸 · Trigger
You want to say the subject cannot do something — no method, no way through.
序 · The move
1Name the subject and the action it cannot carry out.Is this an inability, not a refusal or a ban?
2Place 無法 directly before that verb phrase.Does a full verb follow, never a bare noun?
3Read it back as 'has no way to [verb]'.Would 沒辦法 say the same thing in plainer speech?
例 · Examples
1王美美是一個很愛乾淨loves cleanliness的人，無法has no way to; cannot忍受bear, endure一點髒亂mess, filth。
Wang Meimei is someone who loves cleanliness; she cannot bear the slightest mess.
界 · Boundary
不能
不能 covers permission and circumstance alike (not allowed / can't right now); 無法 is the harder claim that there is no way through at all.
沒辦法
沒辦法 is the everyday spoken twin; 無法 carries the same move in written, formal register.
不會
不會 is lacking the skill (haven't learned it); 無法 is having no way through even when able.
她無法乾淨 ✗ → 她無法保持乾淨 ✓ (無法 needs a verb after it, not a bare adjective/noun)
我無法書 ✗ → 我無法看書 ✓ (put the action verb after 無法)
不無法 ✗ → 無法 ✓ (無法 is already the negation; do not stack 不 in front)
English 'cannot' merges 'not allowed', 'don't know how', and 'no way to'. 無法 only carries the last one — no method exists — so reaching for it whenever you would say 'can't' overshoots into the permission and skill cases that want 不能 or 不會.