grammar → 由
TSUMUGU · TBCL 4 (est.) · 語法
由 grammar point · tier 1 · source 由 (from a starting point, written register)
· yóu
From: marks the point a change or process sets out from, in a written or formal span.

字源 FORM what the parts do

A closed 田-shape with one stem rising through the top. The word it writes is the source: where a thing sets out from.

故事 STORY a scene to remember it by

A shoot breaks the field's crust and climbs; the root stays pinned in the soil it rose out of.
字源記憶法自撰
框 · Frame
[subj] 由 [start] [verb of change] 到 [end]
觸 · Trigger
You want to name the reading a value sets out from as it changes, in a written or measured span.
序 · The move
1Put 由 before the starting reading, ahead of the verb of change.Is what follows 由 the point left behind, not the point reached?
2Carry the change to its endpoint with 到 (降到, 增加到, 改為).Does an endpoint close the span 由 opened?
3Keep the register formal or written; in everyday speech reach for 從.Would this sit in a report or notice, not a casual remark?
例 · Examples
1深夜山上的溫度temperature由from (start point)十度降到drop to (end point)零度以下。
Late at night the temperature on the mountain dropped from ten degrees to below zero.
界 · Boundary
從
由 leads written, formal source spans of a changing value (溫度由十度降到零度); 從 is the everyday spoken origin of a physical motion (從家裡走出來). Same job, split by register and by what moves — a measured change against a person walking.
由 (agent, 'by')
Source 由 names a starting reading a change leaves from; agent 由 names who carries an action out (這件事由我來辦, handled by me). One marks the start point, the other marks the doer.
endpoint dropped: 溫度由十度降。 → 溫度由十度降到零度以下。
ends flipped: 溫度由零度降到十度。 → 溫度由十度降到零度。
everyday motion forced onto 由: 我由家裡走出來。 → 我從家裡走出來。
English 'from' is a single word for every register and both spoken and written use; Chinese splits the start marker, sending the formal changing-value span to 由 and the plain spoken motion to 從.
關 · Related
從1從 is the everyday spoken origin of a motion; 由 marks the same start point in a written, formal span.從…到…從…到… spans a start to an end in speech; 由…到… runs the same span in the written register.向向 orients at the target reached; 由 names the point set out from.