A "However" Sandwich

Too often I see sentences mispunctuated like these:

1. WRONG He arrived at the auditorium 14 minutes after the start of the meeting, however, he found a seat and listened attentively.

2. WRONG He arrived at the auditorium 14 minutes after the start of the meeting, however he found a seat and listened attentively.

Each of these sentences consists of an independent clause, then the conjunction “however,” and then another independent clause.

When “however” is sandwiched between two independent clauses, it requires a semicolon either before or after it.

Why?

In the following passage, from (House & Garden magazine, March 1991, p. 28), notice the second sentence:

3. “My work is like a diary,” Picasso told me, and I have taken him up on this. One has to tread carefully, however. Diaries are nonetheless interesting for embroidering upon the truth. --John Richardson

The second sentence ends, quite correctly, with “however.” “However” is one of the conjunctions that may either begin or end its clause.

If “however” appears between two independent clauses, the reader needs to know whether it ends the first clause or begins the second one. This information is provided by the semicolon:

4. He arrived at the auditorium 14 minutes after the start of the meeting; however, he found a seat and listened attentively.

Of course, it is also correct to split that sentence into two:

5. He arrived at the auditorium 14 minutes after the start of the meeting. However, he found a seat and listened attentively.