By the end of the 19th century it was becoming apparent that electricity had
an intimate relationship with matter.
With **by + a point in time**, the tense depends on whether you're talking
about the **past**, **present**, or **future**.
### 1. By + past time → usually Past Perfect
> **By 1900, scientists had discovered many new elements.**
>
> 到 1900 年時，科學家已經發現了許多新元素。
The action was completed **before** that past time.
---
### 2. By + present time → usually Present Perfect
> **By now, you have probably understood the rule.**
>
> 到現在，你大概已經理解這條規則了。
The action is completed before the present.
---
### 3. By + future time → usually Future Perfect
> **By next year, I will have finished my degree.**
>
> 到明年，我將已經完成學位。
The action will be completed before a future time.
---
### But "by" does not always require a perfect tense
Your example:
> **By the end of the 19th century it was becoming apparent that electricity
had an intimate relationship with matter.**
Here:
* **By the end of the 19th century** sets the historical time frame.
* **was becoming apparent** describes an ongoing process at that time.
* **had an intimate relationship** is not an event that happened before then;
it's a state that existed.
So the writer uses **past progressive** (*was becoming apparent*) rather than
**past perfect**.
Compare:
**By 1900, it was becoming apparent that electricity had an intimate
relationship with matter.**
**By 1900, scientists had discovered the electron.**
The first describes a realization that was unfolding; the second describes a
completed discovery.
A useful rule is:
> **By + time** often goes with a perfect tense when you're emphasizing that
something had already been completed by that time, but other tenses are
possible if you're describing a state, habit, or ongoing process at that time.
--
"A little science distances you from God, but a lot of science brings you
nearer to Him" - Louis Pasteur
https://www.pinterest.com/pin/550494754462794176/
--
※ 發信站: 批踢踢實業坊(ptt.cc), 來自: 220.136.193.205 (臺灣)
※ 文章網址: https://www.ptt.cc/bbs/Eng-Class/M.1781449425.A.CB3.html