One-Letter and Two-Letter Word Deduction Rules in Cryptograms

In grammatical English, an isolated single character is virtually always "A" or "I" (poetic "O" is an extreme rarity). If a single letter appears at the start of a sentence or before a contraction like `'M` or `'D`, it is definitively "I". If it appears before a noun or adjective, it is almost certainly "A".

Over 90% of two-letter words in cryptograms belong to a small group of prepositions, conjunctions, and helper verbs: OF, TO, IN, IS, IT, BE, AS, AT, SO, WE, HE, BY, OR, ON, DO, IF, ME, MY, UP, AN, GO, NO, US, and AM. Notice that almost every two-letter word contains at least one vowel.

If you spot two words that are mirror images of each other (e.g. XY and YX), they are almost always NO and ON. By combining this observation with frequency counts, you can pinpoint both letters simultaneously.