The more I hear people speak and read their writing in all kinds of situations, in real life or in TV/movies, in blog posts, essays, or informal discussion threads, in scripted dialogue or narration or while ad-libbing, the more often I notice however being used as a direct replacement for but, with the same intonation of the voice, cadence of speech, and use of commas as with but. The reason for this is easy to guess: English-speaking students across the world have been misinformed about the appropriateness of various words by at least two generations of pedantic turgidity/formalism fetishists, mainly in English class. Hundreds of millions of people have been taught that But (and its sister conjunction And) absolutely should not, under any circumstances, be used at the beginning of sentences in anything approaching a formal, academic context.
But this admonition is simply wrong. It is pure fantasy. It has no basis in grammar, history, or the traits of polished, edited, formal English prose. It appears in no English style guides in existence. Some person(s) just made it up out of the blue decades ago, presumably to train young students away from starting every other sentence with And. There are editors and entire editing companies (I work for one) that replace every sentence-initial But with However,—and they don’t even do it manually; they run a macro in Microsoft Word that automatically makes this replacement. This is how categorically, inexcusably wrong they see sentence-initial conjunctions. And based on what? It is literally a rule that they, or someone they learned “English” from, conjured up from their own imaginations. Bryan Garner explains why this superstition is completely unfounded. Sentence-initial conjunctions are not less formal, less educated, or less proper or appropriate in any imaginable context or register. Some people just need to get that through their heads and un-learn the misinformation they were inculcated with as youngsters.
In the meantime, until the tide of superstition turns away from this love of sentence-initial However and intolerance of sentence-initial conjunctions, we will continue to see however creep into the proper territory of but in the middle of sentences as well.
I think it’s ironic that this widespread mis-use of however has been caused by the formalism pedants themselves. They hate the mis-use of punctuation around mid-sentence however (so do I), and they hate the appropriation of new meanings or functions by existing words (I do sometimes as well). But their zealotry against sentence-initial conjunctions has had such an effect on self-conscious, unconfident, under-educated English speakers that millions of them now use however as a coordinating conjunction in direct replacement of but, presumably because they want to sound more smart, formal, or fancy. But they don’t. They sound less educated and less competent. It makes it clear that they don’t know the difference between different types of conjunctions (even at a subconscious level), don’t understand the difference between the adverb however and the subordinating conjunction however, don’t know how to use commas and semicolons correctly, and need to rely on turgid formalism instead of the content of their message to have the desired impact on their audience.