King’s engagement with Carlyle was real, not incidental. The 1956 version of The Death of Evil upon the Seashore, preserved by Stanford’s King Institute, quotes Carlyle by name — for a different line, “No lie can live forever” — alongside William Cullen Bryant. That 1956 text contains no reference to Beard and no star saying at all.
The star aphorism appears in the version of that sermon published in the 1963 collection Strength to Love, where King lists Beard’s four laws of history and names Beard as the source. The fourth reads: “when it is dark enough you can see the stars.”
The wording most people now recite as King’s is the one he spoke in Memphis on 3 April 1968, the night before he was killed: “But I know, somehow, that only when it is dark enough, can you see the stars.” That is genuinely his phrasing of the thought — but it is not the sentence at the top of this page.