This study examines the generic characteristics of the detective stories(tales of ratiocination) and their literary educational roles. The tales of ratiocination(reasoning) generally have an entertaining function as a genre of popular novel, that is, providing readers with amusement and relaxation. On the other hand, however, the detective genre requires a very intellectual reasoning of the readers and for this reason the tales of ratiocination are acknowledged as an important bridge of the literary history due to thier transitional status from the popular novel to the serious novel. The tales of ratiocination can be differentiated themselves from the other horror stories(novel of suspense) and crime stories in terms of a presence of a detective in the story and his reasoning(ratiocination), as it is, an action of discovery for a final solution. Holmes and Dupin, two famous detectives, show their way of assumptions, as Semiologist Perce indicates, reasoning of abducion, with diversity including overcoded, undercoded, and creative abduction. Readers also use their own reasoning, various kinds of abduction, in order to solve a problem. The undercoded and creative abductions are very important as they are involved in the probability and originality of the stories. The negative aspect of the detective stories(the tales of ratiocination) should be examined when they are defined as a transitional medium to the serious novel. The characteristic of the detective genre itself is based on the conservative and material viewpoint, though it does not impose this negative ideology upon the readers by force. For example, while the classical detective stories are proceeded by a detective from a noble birth with a very conservative ideology, those of the contemporary hard-boiled detective stories reveal their nihilistic view of the world. For this reason, the critical distance should be required when we read these detective stories.