What's the meaning of "If I could not learn?" in this Thoreau / Walden quote?

Hi, There's a quote from "I went to the woods because I wished to live deliberately, to front only the essential facts of life and see if I could not learn what it had to teach, and not, when I came to die, discover that I had not lived." why did he says "If I could not learn", why... show more Hi,
There's a quote from
"I went to the woods because I wished to live deliberately, to front only the essential facts of life and see if I could not learn
what it had to teach, and not, when I came to die, discover that I had not lived."

why did he says "If I could not learn", why "not"? I know he means if I could learn but
why he used not?
can someone explain it to me please?
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