一來…二來…grammar point · tier 2 · listing reasons 一來…二來… (for one thing … for another …)
Counts off grounds for one conclusion in order: the first reason, then the second, both pointing at the same verdict.
字源 FORM what the parts do
一 is one stroke, the count of one; 二 is two strokes, the count of two — the numerals deal the reasons out in order. 來 is the wheat-graph borrowed long ago to write "come"; the borrowed sound is doing the work here, not the wheat. Tied to each number, 來 brings that counted reason forward. 一來 lays down the first ground, 二來 the next, both feeding the one verdict.
故事 STORY a scene to remember it by
Numbered cards dealt one then two onto the table, each a fresh reason, and all of them point the same way.
One judgment you want to back with two or more separate reasons, counted off in turn.
序 · The move
1Fix the single verdict the reasons all support.One conclusion, several grounds for it — not two unrelated topics.
2一來 + the first reason.A ground that pushes toward the verdict, not a finished action.
3二來 + the next reason (三來 … if more follow).Each later number adds another ground for the same verdict; the count climbs 一→二→三, none outranks the rest.
例 · Examples
1這裡here / this place一來for one thing / first reason沒not have電話phone，二來for another / second reason沒網路internet，聯絡get in touch / contact很不方便very inconvenient。
Here, for one thing there's no phone, for another there's no internet, so getting in touch is very inconvenient.
界 · Boundary
一方面…一方面…
一來…二來… counts grounds for a verdict in numbered order, building a case; 一方面…一方面… holds two faces of one matter level, to weigh rather than to argue. Numbered reasons, not balanced aspects.
一來…二來… stacks two or more reasons before the result; 因為…所以… draws a single cause to its effect. Several grounds counted off, not one cause linked straight through.
不但…而且…
一來…二來… lays each reason level, all feeding the same verdict; 不但…而且… steps up — the second clause outranks the first. Equal grounds, not a climb.
✗ 一來沒電話，沒網路。 → ✓ 一來沒電話，二來沒網路。 (open the second reason with 二來 too, not only the first.)
✗ 因為一來沒電話，二來沒網路，所以不方便。 → ✓ 一來沒電話，二來沒網路，很不方便。 (一來…二來… already carries the reasons; do not also wrap them in 因為.)
✗ 一方面沒電話，二方面沒網路。 → ✓ 一來沒電話，二來沒網路。 (counted reasons take 一來…二來…; 方面 weighs aspects and does not count up to 二方面.)
English 'for one thing … for another …' or 'firstly … secondly …' can leave the reasons loose; learners list the second reason bare or graft on because. Both grounds need their 來 marker, and the marker replaces a separate cause word.