尤其（是）grammar point · tier 1 · especially 尤其(是) — single one out of a set already named
Especially: a set is already in view, and one member of it gets raised above the rest.
字源 FORM what the parts do
尤 is a hand (又) with a stroke laid across it, marking one out from the rest; 又 carries the sound, kept close at yóu. 其 is a winnowing basket whose graph was borrowed (假借) as a pronoun, reading back into the group as among them. Together they reach into a set already named and lift one member clear; 是 names which one when it follows.
故事 STORY a scene to remember it by
A crowd already stands in the frame, and one stroke crosses through to mark the one that stands out.
字源自撰記憶法
框 · Frame
[statement about a whole group], 尤其（是）[the standout member]
觸 · Trigger
A group has been stated; you want to name the one case in it that the point holds for most.
序 · The move
1State the whole group or general case first.Is the set already in view before 尤其 lands? If nothing is named yet, 尤其 has nothing to single out.
2Place 尤其 before the standout member.Is the member one of the set just named, not a fresh topic?
3Add 是 when the standout is a noun or noun phrase being identified.Could the line read as 'it especially is X'? Then 尤其是 fits.
例 · Examples
1百貨公司department store常常often有很多人，尤其是especially (the standout case)週末weekend和假日holiday。
Department stores often have a lot of people, especially on weekends and holidays.
尤其 raises the strongest member out of a set as the prime case; 連…都… drags in the hardest, least-expected member to show the rest follow. 尤其 ranks a top; 連…都… includes an extreme.
特別 marks a thing as unusual on its own, no group required (這件事特別奇怪). 尤其 needs a set already named and singles one out of it.
尤其週末人很多。(no group set first) → 假日人很多，尤其是週末。
我尤其喜歡這個。(no set to single from) → 這些我都喜歡，尤其喜歡這個。
尤其，他很忙。(fronting a fresh topic) → 大家都很忙，尤其是他。
English 'especially' can open a sentence cold ('Especially on weekends...'). 尤其 cannot lead — the general group must be stated first, then 尤其 reaches back into it.