However, this is bad form.
Look at the sentences above, the ones starting with But. Imagine how awful they would sound if the writer had started them with However followed by a comma. No applause for Justice Black if he had written:
The Framers knew, better perhaps than we do today, the risks they were taking. They knew that free speech might be the friend of change and revolution. However, they also knew that it is always the deadliest enemy of tyranny. Hugo Black, The Bill of Rights, 35 N.Y.U. L. Rev. 865, 880-81 (1960).
Avoid starting a sentence with however when the meaning is “nevertheless.” The word usually serves better when not in first position.
Example: The roads were almost impassable. However, we at last succeeded in reaching camp.
Correction: The roads were almost impassable. At last, however, we succeeded in reaching camp.
When however comes first, it means “in whatever way” or “to whatever extent.”
Examples: However you advise him, he will probably do as he thinks best. However discouraging the prospect, he never lost heart. Strunk & White, pp. 48-49.
Strunk & White could have expanded this advice by urging the use of But as a way to start a sentence and to show contrast at its beginning.
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