Solution to 4: Solve This Etaoin-ce

The title clues English letter frequencies (ETAOIN SHRDLU ...) and substitution ciphers; frequency analysis is a technique used to break classical ciphers. The letter frequencies in this text can be mapped on to average letter frequencies as a substitution cipher (TEOSNI... -> ETAOIN...). Putting the first letter of each sentence (as the text suggests) through this cipher yields ISIYT -> NONCE.

There's some ambiguity as to what the average ordering is for less common letters, but the least common letter in NONCE is (definitely) C. The mapping is taken from this page, which is the first Google hit for "english letter frequencies", and is consistent up to C with the Linotype keyboard. Even without the C, using ETAOIN alone gives NON?E which should be enough to get NONCE.

NONCE