How are the poet's feelings about the youth different in Shakespeare's Sonnet XCIV from those of Sonnet XVIII?
One of Shakespeare's most famous sonnets, Sonnet XVIII extoles the quality of love that can transcend the mortality of Nature, while at the same time it recognizes the qualities in nature that refer to the human experience:
Shall I compare thee to a summer's day?
Thou art more lovely and more temperate....
...thy eternal summer shall not fade,
Nor lose possession of that fair thou owest;
This connection of man with nature prevails throughout Sonnet XCIV. However, in this sonnet, the poet is more concerned with the interrelationship as he opens with the observation that the man who exercises restraint protects "nature's riches." In line 9, "summer's flower" is used as a metaphor for human identity and the theme is, then, developed as the poet suggests that if nature's restraint is lost and the flower becomes corrupted ("base infection"), then the weed of evil "outbraves his (the flower's/man's) dignity" and lives while the flower dies.
Thus, in Sonnet XVIII there is absolute confidence that the dignity and beauty of the beloved young man will last forever; however, this eternal dignity is questioned in Sonnet XCIV as corruption can, indeed, cause the ruin of the young man's dignity:
For sweetest things turn sourest by their deed:
Lilies that fester smell far worse than weeds.
It would seem, then, that the poet has become disappointed in the youth and finds himself embroiled in one of the great ironies of the human experience: the object of one's love is often underserving.