A method and apparatus for reducing a set of reference identifiers to a candidate subset of reference identifiers. The reference identifiers are associated in memory with a plurality of index codes. A user provides an input identifier, causing a recognizing device of the present invention to produce a recognized identifier on the basis of the input identifier. The present invention determines an index code based on the recognized identifier and on the basis of a plurality of pre-stored confusion sets of characters that group together in individual confusion sets those characters having a relatively high likelihood of being confused with each other by the recognizing device. After matching the determined index code with one of the reference index codes, the present invention determines which reference index codes are within a predetermined distance of the matched reference index code. The reference identifiers that are associated with these reference index codes constitute the candidate subset of reference identifiers.