Must down: On non-occurring verbs of motion in modern English

Abstract

The first line of what is perhaps the poet laureate John Masefield's best-known poem, "Sea fever", runs

I must down to the seas again, to the lonely sea and the sky

It is a memorable line in a fine poem. One of the things that make it memorable is the use of must down, a phrase with a somewhat quaint ring to it in modern ears.