We focus on the first two tasks. A non-word is a sequence of letters that is not a possible word in the language in any context, e.g., English * thier. Once a sequence of letters has been determined to be a non-word, isolatedword error correction is the process of determining the appropriate word to substitute for the non-word. Given a sequence of letters, there are thus two main subtasks: 1) determine whether this is a nonword, 2) if so, select and rank candidate words as potential corrections to present to the writer. The first subtask can be accomplished by searching for the sequence of letters in a word list. The second subtask can be stated as follows<cite> (Brill and Moore, 2000)</cite> : Given an alphabet Σ, a word list D of strings ∈ Σ * , and a string r / ∈ D and ∈ Σ * , find w ∈ D such that w is the most likely correction.