conj — adds a second, same-direction reason on top of the first: besides, what's more.
字源 FORM what the parts do
再 is 一 over 冓 written short: the double raised one more time, again. 說 is words (言) that lay a thing open; 兌 carries the sound. Together: one more thing said, set on top of what was already said.
故事 STORY a scene to remember it by
One reason lies on the table. A second reason comes down on top of it, pressing the same way.
字源記憶法
框 · Frame
[reason 1] ，再說 [reason 2] 。
觸 · Trigger
First reason is down; you want to pile a second reason that pushes the same conclusion.
序 · The move
1State reason 1 as a full clause.Does it already lean toward the conclusion on its own?
2Open the next clause with 再說.Is reason 2 pushing the SAME way, not turning against reason 1?
3Land reason 2, often with 也 / 又 echoing the addition.Could both reasons stand without each other? If reason 2 only modifies reason 1, 再說 is wrong.
例 · Examples
1他he對看電影watching films沒興趣，再說besides, what's more生意business這麼忙this busy，他也also (echoes the addition)沒時間has no time。
He's not interested in movies; besides, business is so busy he wouldn't have the time either.
而且 adds any further point, written or spoken, neutral. 再說 specifically adds a back-up REASON in talk, often clinching an argument; it leans on the listener.
因為 marks the cause that drives the result. 再說 adds a SECOND, independent reason after the first is already stated, not the result of it.
✗ 再說他很累，所以他不去。 → ✓ 因為他很累，所以他不去。 (a single cause→result needs 因為, not the additive 再說)
✗ 我不想去，再說我很想去。 → ✓ 我不想去，可是我很想去。 (再說 cannot introduce a reason that turns against the first; that is a contrast)
✗ 再說，這本書很有意思。 → ✓ 這本書很有意思。 (再說 needs a first reason already on the table; it cannot open the very first point)
English 'and besides' can drop in even where the two clauses contrast; 再說 only stacks reasons that agree, so an English 'besides' before a contrast must become 可是 / 不過.