Across the floors of silent seas...

The Love Song of J. Alfred Prufrock
T.S. Eliot

In this poem, there is a stanza that reads,

"For I have known them all already, known them all:--
Have known the evenings, mornings, afternoons,
I have measured out my life with coffee spoons;
I know the voices dying with a dying fall
Beneath the music from a farther room.
So how should I presume?'

This is such an interesting passage, as the speaker is saying that he measures his life in the normal, everyday things. It also reminds me of the song, "Seasons of Love," from the musical RENT. The people in the musical sing about how they measure their lives in the things they do every day and in the normal things: daylight, sunsets, midnights, cups of coffee, inches, miles, laughter, and strife. This stanza also shows how the speaker, even though he is young, believes that he has seen all that there is to see. He already "knows them all" and he already knows everything he'll ever need. He knows death and it seems as if he isn't phased by death because he follows "voices dying" with something about music.
"Voices dying" could also mean that ideas are dying. The speaker could be saying that he has seen ideas grow and die, things change, and people lose their convictions. He knows that things will always be the way they are, and that radical changes are not coming in the near future.