Certain letters are more common in written English than others, for example I is used far more often than W. By analyzing a large piece of known text we can find which letters are used most often. These sequences will vary depending on the text analyzed, but typical sequences are :

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

Just as letters have expected frequencies in language, so do groups of letters; tables of frequencies of digraphs (pairs of letters) and trigraphs (sets of three letters) exist to assist the cryptoanalyst. The thirty most common digraphs in the English language are, in order of occurrence:

th, er, on, an, re, he, in, ed, nd, ha, at, en, es, of, or, nt, ea, ti, to, it, st, io, le, is, ou, ar, as, de, rt, ve.

The fifteen most common trigraphs are:

the, and, tha, ent, ion, tio, for, nde, has, nce, edt, tis, oft, sth, men

Other statistics:

Order Of Frequency Of Most Common Doubles ss ee tt ff ll mm oo

Order Of Frequency Of Initial Letters T O A W B C D S F M R H I Y E G L N P U J K

Order Of Frequency Of Final Letters E S T D N R Y F L O G H A K M P U W

One-Letter Words a, I.

Most Frequent Two-Letter Words of, to, in, it, is, be, as, at, so, we, he, by, or, on, do, if, me, my, up, an, go, no, us, am

Most Frequent Three-Letter Words the, and, for, are, but, not, you, all, any, can, had, her, was, one, our, out, day, get, has, him, his, how, man, new, now, old, see, two, way, who, boy, did, its, let, put, say, she, too, use

Most Frequent Four-Letter Words that, with, have, this, will, your, from, they, know, want, been, good, much, some, time

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