The nymph's reply can be read as carrying a realistic, practical tone. The shepherd has painted an impossible scenario and the nymph is pointing out that she is aware of this: "flowers do fade..." and "Thy gowns, thy shoes...soon break, soon wither, soon forgotten..." She understands that love is more than the fleeting possessions one gives to another. She also understands the ways of the world, in that she isn't going to be duped into believing that new love stays the same; like the seasons, love changes (fades): "A honey tongue, a heart of gall/Is fancy's spring, but sorrow's fall." The nymph is right up front about not believing the promises that the shepherd offers when she says, "If all the world and love were young,/And truth in every shepherd's tongue..." she would live with him and be is love. Of course, she knows there is no truth in every shepherd's tongue, as she illustrates in the rest of the poem.
IN lines 1-8 , the tone is hypothetical or supposing. Exploring the possibilities of the vision of the shepherd.
In lines 9-16, the tone shifts to mock with the use of rhyming, alliteration, and words with double meanings.
In lines 17-24, the nymph's tone returns to hypothetical or contingent.
The Nymph's reply is rings of sarcasm and possibly a tinge of regret.
The Shepherd has offered her many things to "come live with me and be my love." However, the Nymph's response includes her pointing out that all of the things the Shepherd has offered her are temporary. All die, dry up, fall apart...nothing he has offered has any staying power. That includes his proclamation of "love". He never mentions marriage. It's more of a "lust" call than a love proclamation.
She says that IF she could be sure that time would stand still and all these flowers and homemade items could last forever with the Spring/Summer months, then she might consider the temptation. However, since she knows it is not true, and he has not offered a commitment past three-four months, she's not biting.
This tone is sardonic, Ralegh is through with the Victorian convention, and line by line debunks the myth with a brutal depiction of reality. From a biographical reading this poem marks a shift in thinking and a desire to move towards a more realistic and modern protrayal of love, beauty, and courtship. No longer will Ralegh elevate the feamle with endless Petrarchan conceits, the author becomes a catalyst for a more practical vision of love and most importantly, demostrates the facts that beauty does not last, time changes all, and love is more than the external. A feminsit reading is easily accomplished when contrasting the Marlowe poem with Ralegh's reply and a new criticism would pontificate the thematic of a practical depiction of love, time, and beauty.