Unquote #8 answer

The quote

I am no bird; and no net ensnares me: I am a free human being with an independent will.

The puzzle as it was set

E IR MH YEXO; IMO MH MPV PMLMIXPL RP: E IR I WXPP BQRIM YPEMU ZEVB IM EMOPAPMOPMV ZENN.

The key

Each code letter stood for one real letter (code letter, then the real letter it hid):

I → AY → BO → DP → EW → FU → GB → HE → IN → LR → MM → NH → OA → PX → RL → SV → TQ → UZ → W

The most frequent code letter was M (12 times), which stood for N. Short words, apostrophes and repeated letters are the usual way in: a one-letter word is almost always A or I, and THE is the commonest three-letter word in English.