The structure of any language enables cryptanalysts to see patterns that emerge from normal messages. Just by looking at a paragraph of text, one can figure out which letters are most common.

In the English language, vowels and spaces are the most frequent characters. A few constants and a few known bigrams (2 letters combination) are more common than others. By recognizing patterns in ciphers one can often guess what the letters are decipher the message.

These are letters in English, in order of most comon to least common:

1. E
2. T
3. A, O, N, R, I, S
4. H
5. D, L, F, C, M, U
6. G, Y, P, W, B
7. V, K, X, J, Q, Z

Besides letter frequency, knowing the frequency of most likely occurring sequence of letters in the particular language may be proven handy as well. In English language, these are sequences in order from most common to least common:

   Bigram of Different letters:
   TH, HE, AN, RE, ER, IN, ON, AT, ND, ST, ES, EN, OF, TE

   Bigram of Same Letters:
   LL, EE, SS, OO, TT, FF, RR, NN, PP, CC, MM, GG

   Trigram (from most common to least common):
   THE, ING, CON, ENT, ERE, ERS, EVE, FOR, HER, TED, TER, TIO, VER

Most frequently occurring words have the following characters:

   Initial Letters:
   T, A, O, M, H, W, C, I, P, B, E, S

   Second Letters
   H, O, E, I, A, U, N, R, T

   Third Letters
   E, S, A, R, N, I

   Final Letters
   E, T, S, D, N, R, Y, G

NOTE:

• More than 50% of English words end with "E."
• More than 50% of English words start with T, A, O, S, or W.