Can "hence" be used at the beginning of a sentence?

Solution 1:

You can use hence at the beginning of a sentence, but not like that. Because it means "therefore", it needs to come after the cause. If you want a conjunction that can come before the cause, use since.

Since I am not feeling well, I am unable to work.

I am not feeling well, hence I am unable to work.

I am not feeling well; therefore, I am unable to work.

I am not feeling well. Hence, I am unable to work.

I am unable to work since I am not feeling well.

Like Neil Coffey said, hence can sound a bit formal. (I wouldn't say it's very formal, just a bit more formal than, say, since.) I think the most natural-sounding way to tell your boss you're sick would be something like:

I'm not feeling well, so I can't come in today.

Solution 2:

I'd rather write your example using since like:

Since I'm not feeling well, I'm unable to work.

"Hence" is a synonym of "therefore", "consequently", "because of that", etc, and being a conjunctive adverb that connects a main clause and a subordinate one, it should appear within the subordinate:

I'm not feeling well; hence, I'm unable to work.

You put a semicolon and a comma after like that, but there are also other ways. I'll edit if I find good examples. If someone can integrate, feel free to do it.

Solution 3:

Something no one has pointed out here.

Hence can also be followed directly by a noun. Examples:

He is sick, hence his absence.

It is winter, hence the snow.

I just received a promotion at work, hence the new car.

His mother was a piano teacher, hence his interest in classical music.

In all of these, the second clause is the situation or thing being queried and the first gives an explanation/reason as to how it arose.