Question: I'm not sure what this sentence means. My dictionary lists 以 as having an adverb-like function of indicating purpose or result so my best guess in translation would be "A vassal intending to kill/having killed his lord, can this be called 仁?" 

Is this even remotely correct? Is there any way to disambiguate purpose and result without further context? 

Also, what is the relationship of this 以 to the other 以 in a sentence like 王以舟去國, "The king left the state on a boat". Are they etymologically related or two different words pronounced similarly or unknown?

Answer: 
EDIT: I didn't realize that there were typos in the quotation:

> 
> The original one should be ~~臣~~ 以**臣**弑君、可謂仁**乎** ~~呼~~
> 
> 
> 

I suppose 臣以弑君 might be an uncommon variant, but it is still grammatical.

---

臣**以**弑君 = **以**臣弑君 killing his lord **as** a vassal.

以 is used as a preposition “as” but the word order is reversed, making it looks like a post-position. The sentence structure is similar to 以下犯上 and 以弱胜强

~~You can also think this 以 means “and”, so 臣以弑君 meaning “being a vassal but killing his lord”.~~ *Although it's common to see 以 be used as “and”, I cannot think of any examples of using 以 as “but”. When I wrote this, I just thought 以 and 而 are sometimes interchangeable. e.g. 臣而弑君 sounds fine to me, which is similar to “人而不仁”, “人而无信”, “君而知礼” ... But 人以无信, etc. do not sound good.*

I think either interpretation doesn't make much difference.

以 originally meant “take” or “use” and was later used as a preposition meaning “by”, “through”, “via”, “with” “because”, etc. e.g.

```
王以舟去國 (by the way, where does this sentence come from?)

```

It's also common to put the object before it, e.g. 

```
仁以為己任 = 以仁為己任, take 仁 as one's responsibility

```

However, 何以 and 是以 almost never become 以何 and 以是.

Sometimes the object 是 (this) or 之 (it) does not appear at all, which makes 以 look like a conjunction meaning “in this way”, “because of this”, “in order to” or “then”.

```
溫故而知新，可以為師矣

```

Sometimes, the original meaning of 以 becomes totally lost and 以 becomes a pure conjunction meaning “and”, which is similar to 而.

```
夫夷以近，則遊者眾；險以遠，則至者少。

```
First, the sentence is incorrect, although your translation is correct. I don't know whether it's a typo or that you read it from an inaccurate source. But the correct version is "以臣弑君、可謂仁乎", as you can find [here](http://baike.baidu.com/view/256577.htm).

Given the correct sentence, I disagree with Yang Muye here. First, “以” doesn't have a meaning equal to "but". Refer to dictionaries of ancient Chinese to verify this fact. The meaning of “以” here, in my opinion, can be roughly translated to "as", "with the identity of", as an extension of its original meaning "using", "with the help of". It's more or less same as “王以舟去国”.

Second the original sentence *certainly* doesn't mean the same as "以下犯上 and 以弱胜强". “以下犯上” means "revolting against your superiors.", while not necessarily between vassal and lords. “以弱胜强” is even more totally different. It means "winning with ostensibly lesser power", for example if you win a war with 5k soldiers against 50k soldiers, then it's “以弱胜强”. It's a positive word, while the previous two are mostly with negative connotations.

P.S.: I don't really think "君臣“ can be translated as "vassal" and "lord". There is hardly a western equivalent for this concept, though a more or less more appropriate one would be "king" and "chancellor". 

Also, the usage of this kind of auxiliary verbs like “以” is extremely diffuse. It has 18 meanings in [this](http://www.zdic.net/z/15/js/4EE5.htm) dictionary. Many auxiliary words in ancient Chinese just don't have concrete meanings. It happens a lot. Don't let such words get into your understanding of articles. If you can make sense of what's going on, just don't tangle on specific words. It's fine. We had to identify specific words in our high school Chinese to an unhealthy extent, which is quite a waste of time.