It is well known that when the reporting verb is in the past， its complement clause also takes a past tense. However，a present tense could be employed as a marked choice. Assuming that what is the most influential in tense choice is the speaker's attitude, this study aims at explaining i) what kind of factors the speaker makes use of, and ii) with what sort of attitude he or she reports the message.
The first and most powerful factor is the semantic relation between the reporting verb and the message in the complement dause. The reporting speaker can choose either present tense or past tense if he or she has a responsibility for the truth value of the message. This might be contrary to the normal semantic relation between the reporting verb and the reported message. The second factor is the syntactic relation between the reporting clause and the complement clause. The third factor, the involvement of the participants in the reporting, encourages the reporting speaker to employ past tense in order to make the message contemporary with the past reporting verb.
In sum, the preference for a present or a past tense is decided by the reporting speaker's judgment of how much responsibility he or she has, regarding the truth value of the reported message.