The hysteron proteron (from the Greek: ὕστερον πρότερον, hýsteron próteron, "latter before") is a rhetorical device. It occurs when the first key word of the idea refers to something that happens temporally later than the second key word. The goal is to call attention to the more important idea by placing it first.
An example of hysteron proteron encountered in everyday life is the common reference to putting on one's "shoes and socks,” rather than "socks and shoes."
By this deliberate reversal, hysteron proteron draws attention to the important point, so giving it primacy. Hysteron proteron is a form of hyperbaton, which describes general rearrangements of the sentence.
It can also be defined as a figure of speech consisting of the reversal of a natural or rational order (as in “then came the thunder and the lightning”) 
Hysteron proteron in poetry
In addition to the traditional use, hysteron proteron is often cited modernly as the usage of a succinct sentence in poetry as a transition between two interposed points and to emphasize the relationship between them or as one line equivocal of two structurally larger paragraphs. This is oft used by the revered poet Matthew Arnold; the seminal example of this is the transitional line between stanzas 1 and 4 in the episcopalian "To Marguerite—Continued," Arnold's ruminative, metaphysical commentary on mental isolation; "Across the sounds and channels pour --... But how long we walk without the moon, one of speckling and sparkling sheen... Oh! then a longing like despair". 
- Smyth, Herbert Weir (1920). Greek Grammar. Cambridge MA: Harvard University Press. pp. 679–680. ISBN 0-674-36250-0.