What is a summary of Shakespeare's "Sonnet 18''?

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melissamd eNotes educator| Certified Educator

This is one of Shakespeare's sonnets in which he gives "advice" to a young man, one he is apparently mentoring.  In various sonnets he gives him advice on love, money, etc.  This particular sonnet finds Shakespeare amazed and ashamed that the young man seems to have no love in his heart, only hatred.  In the first quatrains he asks the young man about this hatred, seeming to seek clarification that man really is so hateful.  In the second quatrain he compares the young man's hate to a house--the man hates so much that he does not even repair the roof of his home (i.e. himself).  If he takes such poor care of his home (himself) it will fall in, and perhaps kill him.  By the final quatrain Shakespeare is pleading with the young man to change his ways, or prove Shakespeare wrong.