<p>In old saying, 以 could mean 在 or 于. For example, 余以3月1日返：I returned on March 1st. </p>

<p>Refer to the definition 4 in <a href="http://www.zdic.net/z/15/js/4EE5.htm" rel="nofollow noreferrer">this dictionary</a>. </p>

<p>However, nowadays, we don't usually use 以 for this kind of purpose any more. Instead, 于 or 在 is more common. But you could possibly hear it in those old movies. 余以3月1日返 is classic literature, and people might apply this usage of 以 when they write a classic essay, novel, and etc.  </p>

CC BY-SA 3.0
2017-10-27T23:00:07.450Z
2017-10-27T23:00:07.450Z
dan
<p>As a preposition, 以(with)  and 于(at/ in) are very different.</p>
<blockquote>
<p><em>我以三月一日返。</em>(I take March the first come back)</p>
<p>It is plain wrong, the sentence make no sense.</p>
</blockquote>
<p>The only way you can use 以 with a fixed date or period of time is:</p>
<ol>
<li><p>In a [<strong>以</strong> (A) <strong>为</strong> (B)] structure -- Example: &quot;<strong>以</strong>三月一日<strong>为</strong>限期&quot;  (<strong>take</strong> March the first <strong>as</strong> the deadline)</p>
</li>
<li><p>use '以' as preposition 'with' -- Example: &quot;<strong>以</strong>三日时间完成这工作&quot; (finish this job <strong>with</strong> three days time)</p>
</li>
</ol>
<blockquote>
<p><em>生于上海 (born <strong>in</strong> Shanghai)</em> is correct</p>
<p><em>来信与十五日收到</em>。There must be a typo. It should be &quot;来信<strong>于</strong>十五日收到&quot; (your letter arrived <strong>at</strong> the fifteen)</p>
</blockquote>
<p><strong>于</strong> can be a preposition for <strong>date</strong> or <strong>location</strong></p>
<p>Example:</p>
<p>&quot;生<strong>于</strong>上海&quot; (born <strong>in</strong> Shanghai) - <em>location</em></p>
<p>&quot;生<strong>于</strong>一九一二年&quot; (born <strong>in</strong> 1912) - <em>date</em></p>
<p>&quot;<strong>于</strong>上午五点死亡&quot; (died <strong>at</strong> 5:00 AM) - <em>time</em></p>

CC BY-SA 3.0
2017-10-27T18:04:49.963Z
The example sentence is from Pleco, FYI.
Blaszard
CC BY-SA 3.0
2017-10-27T18:14:08.147Z
Trust me, a living person who speak Chinese as his first language, 我以三月一日返 is grammatically incorrect; 与 in 来信与十五日收到 is a typo for 于. You can ask one hundred more people and they will all agree with me.
Tang Ho
CC BY-SA 3.0
2017-10-28T03:45:04.467Z
This usage of 以 only exists in ancient texts, today it's just grammatically wrong
Jason Swift
CC BY-SA 3.0
2017-10-28T06:50:22.860Z
We shouldn't say it's grammatically wrong as of now, because you can still see the usage of 以 in 新华字典. So, it seems that it has not been obsolete completely yet.
dan
CC BY-SA 3.0
2017-10-27T18:03:51.240Z
2017-10-27T18:08:37.703Z
2020-06-17T09:50:11.587Z
Tang Ho
<p>我以三月一日返 sounds like some Classical Chinese thing.</p>

<p>It is not able to compare with Modern chinese.</p>

<p>So you must translate it to "Chinese" first.</p>

<p>If you do so, this sentence will be “我于三月一日返回” or “我以三月一日为返回的期限”.</p>

<p>note the secound usage is “以X为Y”, not related with time.</p>

CC BY-SA 3.0
2017-11-01T10:06:11.853Z
2017-11-01T10:06:11.853Z
GongT
<p>Here is another example of using 以 as &quot;at&quot; : 山区的石灰岩层，以大约三十度的角度，由南向北斜. The limestone layer in the mountain area slopes from south to North at an angle of about 30 degrees</p>

CC BY-SA 4.0
2021-08-25T23:28:23.570Z
The example may not be quite related to the question.
L Parker
CC BY-SA 4.0
2021-08-24T15:59:20.063Z
2021-08-24T15:59:20.063Z
Irakly Chichua
<p>I learned that 以 can also function to mean &quot;a certain time&quot; or &quot;a fixed date&quot;, for example:</p>
<blockquote>
<p>我以三月一日返。</p>
</blockquote>
<p>However, I also know that 于 can work in the same purpose, for example:</p>
<blockquote>
<p>生于上海</p>
<p>来信于十五日收到。</p>
</blockquote>
<p><sub><em>All the example sentences are from Pleco.</em></sub></p>
<p>I feel that in these usages, 以 is used only to express &quot;time&quot;, and not &quot;place&quot;. So 生以上海 is wrong.</p>
<p>However, if it means &quot;a fixed date&quot;, is there any difference (and if it is what is it) between 以 and 于?</p>
<p>Also, is there any such prepositions that function for the same purpose?</p>

CC BY-SA 3.0
2017-10-27T17:52:04.240Z
see dictionaries,bkrs：于= 於 universal prep. of literary language, in, on, at; the other two have many other meanings, quoted examples may indicate low frequency usage
  **生于上海**  ：① 介词。
a>在：她生于1949年│黄河发源于青海。
b>向：问道于盲│告慰于知己│求救于人。
c>给：嫁祸于人│献身于科学事业。
d>对；对于：忠于祖国│有益于人民│形势于我们有利。
e>自；从：青出于蓝│出于自愿。
f>表示比较：大于│少于│高于│低于。
g>表示被动：见笑于大方之家。
   **我以三月一日返**  ；以 at (a certain date or place) ,
    **来信与十五日收到**  :与:and; with; to; for;22) 介词。同，跟。
23) 介词。以。
24) 介词。替。
25) 介词。把；将。
26) 介词。被。
27) 介词。於；在。
28) 介词。向。
29) 介词。从；由。
user6065
CC BY-SA 3.0
2017-10-27T18:19:24.087Z
与 placed before verb／adjective： 与学生谈，心与柏石坚，与你没关系，与困难作斗争，其衣与花借色，请你与我对他致谢， 于 after verb：用于，出于，处于，在于，相当于，。。。
user6065
CC BY-SA 3.0
2017-10-27T18:52:38.373Z
以 bkrs 6) indicating time:
壮者, 以暇日修其孝弟 (tì) 忠信,  
其弟 (dì) 以千亩之战生  
⑤ 〈书〉于；在<时间>：中华人民共和国以1949年10月1日宣告成立  ichacha: 以 [书面语] (于; 在) at (a certain time); on (a fixed date) 短语和例子
user6065
CC BY-SA 3.0
2017-10-27T19:19:50.457Z
与 is a typo, I fixed it just now.
Blaszard
<difference><word><preposition>
What is the difference between 于 and 以 to express "a certain time" or "a fixed date"?
# What is the difference between 于 and 以 to express "a certain time" or "a fixed date"?

(Asked by: username_0 on 2017-10-27)

I learned that 以 can also function to mean "a certain time" or "a fixed date", for example:

> 我以三月一日返。

However, I also know that 于 can work in the same purpose, for example:

> 生于上海
>
> 来信于十五日收到。

*All the example sentences are from Pleco.*

I feel that in these usages, 以 is used only to express "time", and not "place". So 生以上海 is wrong.

However, if it means "a fixed date", is there any difference (and if it is what is it) between 以 and 于?

Also, is there any such prepositions that function for the same purpose?

**Tags:** difference, word, preposition
> **Comments:**
> **username_1**: see dictionaries,bkrs：于= 於 universal prep. of literary language, in, on, at; the other two have many other meanings, quoted examples may indicate low frequency usage   **生于上海**  ：① 介词。 a>在：她生于1949年│黄河发源于青海。 b>向：问道于盲│告慰于知己│求救于人。 c>给：嫁祸于人│献身于科学事业。 d>对；对于：忠于祖国│有益于人民│形势于我们有利。 e>自；从：青出于蓝│出于自愿。 f>表示比较：大于│少于│高于│低于。 g>表示被动：见笑于大方之家。    **我以三月一日返**  ；以 at (a certain date or place) ,     **来信与十五日收到**  :与:and; with; to; for;22) 介词。同，跟。 23) 介词。以。 24) 介词。替。 25) 介词。把；将。 26) 介词。被。 27) 介词。於；在。 28) 介词。向。 29) 介词。从；由。  
> **username_1**: 与 placed before verb／adjective： 与学生谈，心与柏石坚，与你没关系，与困难作斗争，其衣与花借色，请你与我对他致谢， 于 after verb：用于，出于，处于，在于，相当于，。。。  
> **username_1**: 以 bkrs 6) indicating time: 壮者, 以暇日修其孝弟 (tì) 忠信,   其弟 (dì) 以千亩之战生   ⑤ 〈书〉于；在<时间>：中华人民共和国以1949年10月1日宣告成立  ichacha: 以 [书面语] (于; 在) at (a certain time); on (a fixed date) 短语和例子  
> **username_0**: 与 is a typo, I fixed it just now.  

---

## 4 answers

### Answer by username_2 on 2017-10-27. Score: 1 | Accepted answer

In old saying, 以 could mean 在 or 于. For example, 余以3月1日返：I returned on March 1st.

Refer to the definition 4 in [this dictionary](http://www.zdic.net/z/15/js/4EE5.htm).

However, nowadays, we don't usually use 以 for this kind of purpose any more. Instead, 于 or 在 is more common. But you could possibly hear it in those old movies. 余以3月1日返 is classic literature, and people might apply this usage of 以 when they write a classic essay, novel, and etc.


---

### Answer by username_3 on 2017-10-27. Score: 2

As a preposition, 以(with) and 于(at/ in) are very different.

> *我以三月一日返。*(I take March the first come back)
>
> It is plain wrong, the sentence make no sense.

The only way you can use 以 with a fixed date or period of time is:

1. In a [**以** (A) **为** (B)] structure -- Example: "**以**三月一日**为**限期" (**take** March the first **as** the deadline)
2. use '以' as preposition 'with' -- Example: "**以**三日时间完成这工作" (finish this job **with** three days time)

> *生于上海 (born **in** Shanghai)* is correct
>
> *来信与十五日收到*。There must be a typo. It should be "来信**于**十五日收到" (your letter arrived **at** the fifteen)

**于** can be a preposition for **date** or **location**

Example:

"生**于**上海" (born **in** Shanghai) - *location*

"生**于**一九一二年" (born **in** 1912) - *date*

"**于**上午五点死亡" (died **at** 5:00 AM) - *time*

> **Comments:**
> **username_0**: The example sentence is from Pleco, FYI.  
> **username_3**: Trust me, a living person who speak Chinese as his first language, 我以三月一日返 is grammatically incorrect; 与 in 来信与十五日收到 is a typo for 于. You can ask one hundred more people and they will all agree with me.  
> **username_4**: This usage of 以 only exists in ancient texts, today it's just grammatically wrong  
> **username_2**: We shouldn't say it's grammatically wrong as of now, because you can still see the usage of 以 in 新华字典. So, it seems that it has not been obsolete completely yet.  

---

### Answer by username_5 on 2017-11-01. Score: 0

我以三月一日返 sounds like some Classical Chinese thing.

It is not able to compare with Modern chinese.

So you must translate it to "Chinese" first.

If you do so, this sentence will be “我于三月一日返回” or “我以三月一日为返回的期限”.

note the secound usage is “以X为Y”, not related with time.


---

### Answer by username_6 on 2021-08-24. Score: 0

Here is another example of using 以 as "at" : 山区的石灰岩层，以大约三十度的角度，由南向北斜. The limestone layer in the mountain area slopes from south to North at an angle of about 30 degrees

> **Comments:**
> **username_7**: The example may not be quite related to the question.  

---

