1. A computer-implemented method comprising: receiving, by a computing device and from an advertiser, a textual representation of a candidate adword for use in a bidding process for selecting advertisements based on a transcription of a speech query; generating, by a text to speech module of the computing device, data that represents an audible representation of the textual representation of the candidate adword for use in the bidding process for selecting advertisements based on the transcription of the speech query; based on the data that represents the audible representation of the textual representation of the candidate adword for use in the bidding process for selecting advertisements based on the transcription of the speech query, generating a transcription of the audible representation of the textual representation of the candidate adword for use in the bidding process for selecting advertisements based on the transcription of the speech query; applying an acoustic model for a speech recognizer to the audible representation of the textual representation of the candidate adword for use in the bidding process for selecting advertisements based on the transcription of the speech query; applying a language model for the speech recognizer to the transcription of the audible representation of the textual representation of the candidate adword for use in the bidding process for selecting advertisements based on the transcription of the speech query; based on applying the acoustic model for the speech recognizer to the audible representation of the textual representation of the candidate adword and based on applying a language model for the speech recognizer to the transcription of the audible representation of the textual representation of the candidate adword, generating, for the textual representation of the candidate adword for use in the bidding process for selecting advertisements based on the transcription of the speech query, a score that reflects a likelihood of the speech recognizer generating, in response to receiving an utterance of the candidate adword, a transcription that includes a word that is associated with the textual representation of the candidate adword; and based at least on the score that reflects the likelihood of the speech recognizer generating, in response to receiving the utterance of the candidate adword for use in the bidding process for selecting advertisements based on the transcription of the speech query, the transcription that includes the word that is associated with the textual representation of the candidate adword, classifying the textual representation of the candidate adword as an appropriate adword for use in the bidding process for selecting advertisements based on the transcription of the speech query or as not an appropriate adword for use in the bidding process for selecting advertisements based on the transcription of the speech query.