Hi Viola, For the most part, they are the same. They both introduce a contradiction from a previous point. However is considered to be more formal and used in academic situations like presentations and writing. Using 'but' in academic writing is usually frowned upon.

Yes, some people joke that "however" is a fancy "but." There is also a difference in punctuation. I have made up these examples: I. I speak English, but I do not speak French.(a comma after "English.") 2. I speak English; however, I do not speak French. (a semi-colon after "English" and a comma after "however."} 3. I speak English. However, I do not speak French. (a period after "English" and a comma after "however.")

I agree with the previous answer. Saying ‘however’ is it a bit too formal for speaking, and writing ‘but’ is definitely too informal for writing.

Viola, yes, "but" can definitely start a sentence. In fact, some of the best writers do so. BUT learners are advised NOT to do so until they are advanced users of the language. Some learners start too many sentences with "but," so it becomes absurd. "But" is often placed at the beginning of a sentence for effect (drama). I have made up this example. It is NOT very good. But maybe it gives you an idea. "I love doughnuts. There's a doughnut shop on my way home from work. I often think about going in and buying a dozen. BUT I don't, (More dramatic or emphatic than "I often think about going in and buying a dozen, but I don't.") P.S. Most Americans now spell "doughnut" as "donut."