«Thy gift, thy tables, are within my brain
Full character’d with lasting memory».
Just as the poet gave a notebook to the youth in Sonnet 77, the youth has given the poet a notebook, which the poet discards.
Thy gift, thy tables, are within my brain
The poet, who knows more about the youth than any book can contain, says that he does not need a reminder of the young man. Rejecting the notebook is a curious gesture, almost uncaring, indicating how casual the relationship has become. Although the last two lines — “To keep an adjunct [aid] to remember thee / Were to import forgetfulness in me” — emphasize that the poet does not fear losing his memory of the youth, the entire sonnet implies that the youth is fast becoming only a dear memory to the poet, if he is not one already.
English audio from YouTube Channel Socratica
Summary from Cliffsnotes.com