是grammar point · tier 1 · emphatic 是 (it really is so / granted, it is)
· shì
Stressed 是 before a whole predicate (often an adjective), granting or affirming that the claim holds true; bare 很 would merely state it.
字源 FORM what the parts do
The sun (日) above, straight (正) below: what stands true under the sun. The same graph that equates two nouns is set under stress and turned on a whole claim, vouching that it holds.
故事 STORY a scene to remember it by
A claim is held up to the noon sun and stands dead straight under the glare; the sun cannot bend it.
字源記憶法
框 · Frame
[subj] 是 [stative/verbal predicate]
觸 · Trigger
You want to grant or affirm that a claim holds — to concede the point before adding a turn, or to confirm it under stress.
序 · The move
1name the subject the claim is aboutis there a predicate you want to vouch for as true, not a second noun to equate?
2set 是 under stress in front of the whole predicatewould the sentence still stand if 是 were dropped? if yes, 是 is the emphatic one, not a copula the grammar needs
3let the predicate run on as normal (adjective keeps its 很, verb keeps its objects)is what follows 是 a full predicate, not a bare noun?
4if a turn is coming, follow with 但是 / 不過concession often pairs 是 … 但是 (granted … but)
例 · Examples
1A：出版旅遊雜誌要花不少錢吧！B：（出版旅遊雜誌的）成本cost是is indeed / granted, it is很高(very) high。
A: Publishing a travel magazine must cost quite a lot! B: The cost (of publishing a travel magazine) is indeed high.
Copula 是 equates two nouns and cannot be dropped (我是學生, never 我學生). Emphatic 是 stresses a whole predicate that already stands on its own (成本很高), and drops without breaking the sentence; it only adds the 'granted, it is so' force.
是…的 closes 的 behind a focused detail of a past event (我是昨天到的). Emphatic 是 takes no closing 的 and vouches for the whole present claim, not one detail of it.
我是高 → 他問你高不高？我是很高 (only emphatic-是 with a stressed full predicate, not 是+bare adjective)
成本是高的 → 成本是很高 (no closing 的; this is emphatic 是, not the 是…的 frame)
成本很高是 → 成本是很高 (是 sits before the predicate, not trailing it)
English carries this with a stressed auxiliary — 'it IS expensive' — and has no separate word, so learners either drop 是 entirely (losing the concession) or wrongly read it as the copula and try to follow it with a noun.