Structurally Donne is unique in the structure of the poem. The poem has a rhythm and a rhyme scheme a,b,a,b,c,c,d,d,d. With lines 7-8 Donne has two word lines which add impact to those words "And find/What wind", "And swear/no where", and "Yet she/Will be".
Donne does not paint a very good impression of women. In the first stanza of the poem, he gives instructions to catch a falling star, get pregnant by becoming fertile with a mandrake's root, explain where years go when they are over and done with. All of these and more are seemingly impossible things that can not be achieved. As well, finding a fair and true woman is equally impossible.
Donne even says if you can find the answer to why the devil has a cleft foot, then you will find a good woman. The unstated message is how can a person discover this answer? The only way is by visiting the devil himself in hell. Perhaps that is where a true woman is.
Donne wants to be taught to hear mermaids singing and yet in mythology mermaids sung sailors to their deaths. With this line Donne appears to say that women simply lead men onto their undoing almost as if men are just unthinking fools easily lured by the evil female. This is a very negative impression of women indeed.
In the second stanza, Donne challenges the reader to gallop on horse back all around the world and only return when a true woman is found. In the end with gray hair and 10,000 days and nights, the quest will still not be met because the prize does not exist.
In the final stanza Donne gives it up to the reader in an "okay, okay, okay" type of manner as if to say, "Fine, I'll admit maybe you found a true and virtuous woman, but as soon as I reach her she would have already been untrue with at least two or three men by then".
In the entire poem Donne never questions the faithfulness of men. It seems a bit ironic that in 16th and 17th century society, women were expected to be chaste and men were able to be as randy as they pleased. Donne does not address whether or not a woman could find a virtuous man. In truth that was probably a more difficult quest.