## Chapter III: Frequency Analysis

Frequency letter substitution codes do not need to use symbols. Letters can just be replaced by other letters. The Caesar Shift code is a very simple letter substitution code. The puzzles you are solving are simple letter substitution codes.

Frequency analysis means counting the number of times each symbol in the cipher occurs. The frequency of the letters in English is:

**E T A O I N S R H L D C U M F P G W Y B V K X J Q Z**

In our Enigma puzzles we show you the letter frequencies of the encrypted text in the blue bars. This is intended to help you decipher the message.