以…為主grammar point · tier 2 · predominantly 以…為主 (take X as the main one)
Frame that ranks one element of a set as the dominant one, the rest subordinate: take X and make it the main thing.
字源 FORM what the parts do
以 opens the bracket, grammar's quiet tool, with the sense take this. 為主 closes it. 為, read wéi, is a hand (爫) leading an elephant (象) by the trunk, the graph for to make into; 主 is a lamp-flame on its stand, the one point of light a whole room turns toward, borrowed for the master, the main thing. 為主 makes the bracketed element the master of its set. Whatever sits between the brackets is the one thing the rest fall in behind.
故事 STORY a scene to remember it by
A room of many lamps, and one set to burn brightest at the centre. Every other light is trimmed low and ranged around it; the eye goes to the one flame first.
字源記憶法
框 · Frame
以 [element X] 為主 (X is the dominant one of a set; the rest are secondary)
觸 · Trigger
Out of several things in play, one carries the weight and the others fill in around it.
序 · The move
1Name the set, then pick the one element that dominates it.Are there other members it outranks? 為主 ranks within a group; with only one thing there is nothing to be main over.
2Drop that element into the bracket: 以 + X + 為主.X is the predominant member, not a label pinned to the subject. If you are assigning X a fixed name or role rather than ranking it, the frame is 以…為… without 主, or 把…當作….
3Attach the whole frame to the subject whose make-up you are describing.Read it back: the subject is mostly X, with other things present but secondary. If nothing else is present at all, 都是 / 全是 fits, not 以…為主.
This country's economy is predominantly agricultural.
界 · Boundary
以…為…
以…為主 ranks X first among several (以蔬菜為主 — mostly vegetables, meat secondary). The bare 以…為… pins a fixed label or role to X (以他為首 — make him the leader, 以此為例 — take this as an example). Predominance vs assignment; only 為主 implies a runner-up.
主要 is an adverb/adjective dropped before what it modifies (主要是農業 — it's mainly agriculture). 以…為主 is a bracketed coverb frame wrapping the element (以農業為主). Same predominance, modifier slot vs frame.
都是 / 全是
都是 says the whole set is X, no exception (這裡都是農田). 以…為主 says X leads but other things remain (mostly farmland, some else). Totality vs majority.
✗ 這裡的人都以中文為主 in the sense everyone speaks only Chinese → ✓ 這裡的人都說中文 (use 為主 only when other languages are also present but minor)
✗ 這家店以賣咖啡為主要 (為主 already closes the frame) → ✓ 這家店以賣咖啡為主
English 'mainly / mostly' is one adverb you can drop anywhere; learners reach for it and stall, or splice it as 主要 before the verb. 以…為主 is a two-piece bracket — 以 must open it and 為主 must close it around the element, the element cannot sit loose.