Although but and however have the same meaning, they are punctuated differently when used to join complete sentences:

• but follows a comma and is not followed by any punctuation
• however follows a period or semicolon and is followed by a comma

For example:

Correct: An increasing number of people at the company bike or take public transit to work, but many employees still prefer to drive.

Incorrect: An increasing number of people at the company bike or take public transit to work. But, many employees still prefer to drive.

Correct: An increasing number of people at the company bike or take public transit to work. However, many employees still prefer to drive.

Correct: An increasing number of people at the company bike or take public transit to work; however, many employees still prefer to drive.

Incorrect: An increasing number of people at the company bike or take public transit to work, however, many employees still prefer to drive.

 

On the surface, the fact that these two words must be punctuated differently might seem odd—the kind of persnickety little rule that tends to give grammar a bad name. However, it actually exists for a reason.

But and however may serve the same purpose within a sentence, namely to introduce a contrasting or opposing idea; however, they come from two different grammatical categories, which have slightly different uses and implications.

But is a coordinating conjunction, i.e., a FANBOYS conjunction (acronym for For, And, Nor, But, Or, Yet, So). These transitions can be used in either informal or formal writing, and they create a sense of continuity rather than a hard stop between two ideas.

However is a conjunctive adverb (along with words such as therefore, moreover, and nevertheless). These transitions create a more formal tone, as well as a stronger division between thoughts. A semicolon indicates a stronger stop than the comma before but does, and a period can also be used to create an even more complete stop.

So the but/however distinction is a matter of style and meaning, not just grammar.

Furthermore, like all conjunctive adverbs, however can be placed either at the beginning of a clause, OR in the middle of a clause, surrounded by two commas (as a non-essential word). In contrast, but cannot be used this way.

So while however can appear like this:

Correct: An increasing number of people at the company bike or take public transit to work. However, many employees still prefer to drive.

It can also appear like this:

Correct: An increasing number of people at the company bike or take public transit to work. Many employees, however, still prefer to drive.

Although however appears in two different places, it has exactly the same purpose in both example: it indicates a contrast between the second sentence and the first sentence—unlike but, it does not connect two halves of the same sentence.

When however is placed after a comma, the implication is that the writer is introducing a contrast with the previous sentence, not with the statement that follows.

If a second comma does not appear, and the contrasting information appears after however, readers must reorient themselves and recognize that however is not being used in the way they were expecting.

Although this process happens very quickly, within a second or so (at least in my own experience), it still interrupts the flow of meaning, and forces the reader to work just a little harder than necessary to figure out what the writer is trying to say.