What is the meaning of "Death's second self" in line 8 of Shakespeare's Sonnet 73?
"Death's second self" refers to night, and is just a continuation of the idea began in that quatrain at line 5:
"In me thou see'st the twilight of such day
As after sunset fadeth in the west,
Which by and by black night doth take away,
Death's second self, that seals up all in rest."
Death and sleep were rather interconnected to the Elizabethans, and Shakespeare uses that motif often in his writing (Hamlet discourses a great deal about death and sleep in his famous "To be or not to be" soliloquy).
The speaker of the sonnet is reminding whoever he is speaking to that his looks, his body, are aging, and he is entering the twilight (darkness) of life in preparation for death.
Check the links below for more information about the sonnets. The link to "themes" is especially good and actually discusses sonnet 73 specifically. Good luck! :)
I have long disagreed with the common interpretation of this sonnet. Although I agree that the images of night, bare trees, etc., are symbols for the passing of time, and that "Death's second self" could simply be a reference to this, I cannot help to think that this poem is about self-love, not the love of another. It is about the sadness of knowing that even the most brilliant of minds can wither and slow down with the passing of time.
Consider these lines as a whole:
"Death's second self, that seals up all in rest.
In me thou see'st the glowing of such fire,
That on the ashes of his youth doth lie,
As the death-bed, whereon it must expire,
Consumed with that which it was nourish'd by."
Death has two states: Its approach and its presence. A mind also only has two states: Thinking and the inability to think. Thinking - his driving life force - marked the speaker’s life. Age slows the mind and even 'death' can appreciate a well-used one.
"Death's second self" refers to sleep. My English teacher who was extrememly knowledgable, asked us to find the meaning in the late 80's. This was, of course, before the day of access to computers. I looked high and low in every library for the meaning because the teacher offered us extra credit for the answer. I finally found it in the local junior college library. When he asked the class if anyone found the meaning, I raised my hand. I told him it meant sleep. He said in the 30+ years that he had been teaching, he had never found one student who looked hard enough to find the answer. I was right....it meant sleep....and I got an A in the class.
"Death's second self" is a replica or a duplicate of death. Death means the end of life and, therefore, complete darkness; and night too means darkness.