grammar → 替
TSUMUGU · TBCL 3 (est.) · 語法
grammar point · tier 1 · benefactive 替 (do something in someone's place, for them)
· tì
Benefactive: do the action standing in someone's place, on their behalf.

字源 FORM what the parts do

Two figures (夫) stand side by side over 曰; one steps down, the next steps up — one taking the other's place. The older graph wrote 竝 over 白 and has worn past clean reading; the two side-by-side figures are what the modern glyph shows, and they carry the swap. To stand in another's place is to act for them: 替我、替你.

故事 STORY a scene to remember it by

Someone leaves their spot empty, and you step into it and carry out what was theirs to do.
推測字源記憶法
框 · Frame
[subj] 替 [person] [verb phrase]
觸 · Trigger
You want to do a task on someone's behalf, taking the place they would have filled.
序 · The move
1Name whose place you step into — the person the action is done for — and put them right after 替.Is the slot after 替 a person, not the thing acted on?
2Put the whole verb phrase — the task that was theirs to do — after that person.Does the subject do this, with the named person standing back?
3If it is a request, close with 嗎 to turn it into a yes-no question.Read it back: subject does it, person is stood in for — not the reverse.
例 · Examples
1你可以tì — for me, in my placethe one the task is done formarks the gift as the thing acted on禮物包起來嗎?
Can you wrap the gift for me?
界 · Boundary
替 stands in the person's place (you do it instead of them, as a substitute); 幫 assists with their task (you help get it done). 替你寫 = I write it in your stead; 幫你寫 = I help you with the writing.
替 names the person you act for (in their place); 向 names the target you act at or toward. 替他問 = ask on his behalf; 向他問 = ask the question to him.
替 takes a person after it (whose place you fill); 把 takes a definite thing after it (the one disposed of). 替他 = for him; 把它 = act on it.
我替禮物包。 → 我替他包禮物。 (the slot after 替 is the person, then the verb phrase)
我替包禮物。 → 我替你包禮物。 (name whose place you step into)
請你替我。 → 請你替我寄信。 (state the task done in their place)
English trails the beneficiary in a tail phrase 'for me' at the end; Chinese fronts it right after 替, before the verb.