簡言之grammar point · tier 1 · 簡言之 in brief / to put it simply (condense what was just said)
In brief: closes off what was just said and restates it in one compressed line.
字源 FORM what the parts do
簡 is one bamboo writing slip (竹 on top), and a slip holds only a line or two; 間 gives it the sound, the tone risen to jiǎn. 言 is a mouth (口) with the breath going out straight — to say. 之 is the classical it, the matter just laid out. The three read in order: say it brief, the it being everything before.
故事 STORY a scene to remember it by
A long speech is pared down to fit one bamboo slip; the slip carries the whole of it in a single line.
字源記憶法
框 · Frame
[full statement]。簡言之，[the same thing said short]。
觸 · Trigger
You have laid something out at length and want to close it with one short restatement of the gist.
序 · The move
1Finish the full statement first; 簡言之 looks backward, so there must be something already said to compress.Is there a complete idea before it for the short line to restate?
2Open the next sentence with 簡言之 and a comma, then give the gist in its shortest form.Does the line after it say the same thing, only pared down — not a new point?
3Keep the restatement tight; the move is brevity, so trim it to the core.Could the short line stand alone as the takeaway if the rest were cut?
簡言之 compresses one stretch of argument into a shorter line (say it brief). 總而言之 gathers several separate points into one closing sum (all of it together). 簡 is paring down; 總 is adding up.
也就是說
簡言之 restates short, written and condensed. 也就是說 restates to clarify or rephrase, spoken and even-length — it does not promise brevity, only that the next line means the same.
簡言之，心情好，抵抗力就強。（無前文） → 假如…就比較可以抵抗病菌的感染。簡言之，心情好，抵抗力就強。 (簡言之 needs the full statement first; with nothing before it, there is nothing to condense.)
心情好，抵抗力就強，簡言之。 → 簡言之，心情好，抵抗力就強。 (簡言之 leads the closing line; it does not trail it.)
簡言之地說，心情好，抵抗力就強。 → 簡言之，心情好，抵抗力就強。 (簡言之 already carries 言 = say; no second 說 is added.)
English drops in brief mid-sentence or after a dash with free placement; 簡言之 is a fixed four-character classical connective that sits at the head of its own clause, set off by a comma, and already contains the verb say (言), so no extra 說 follows.