When I was One and Twenty" was acknowledged by W. B. Yeats to be the inspiration for his poem "Sally Garden".

Since A Shropshire Lad, including Housman's poem, was puiblished in 1896, and Crossways, with Yeats's, was published in 1889, this seems questionable, even though it is true that poems exist in manuscript before they ever get printed.

Given the identical metre, which means the two can be sung as one song, and the similarity of theme it might conceivably be true the other way round. (Though Housman's joke about a 22 year old lamenting the long lost days when he was 21 has no equivaknet in the poem by Yeats - which is a distillation of a pre-existing song he didn't write.)