In Chaucer’s narrative text events usually expressed in the past tense in modern English are more often than not expressed in the present tense. The speaker or subjectivity of cognition is flexible enough to depart from the speech time (absolute present time) to be close to the phenomena in the past, which tends to promote the present tense. Tense shift analysis in Chaucer has so far been limited to the historical present and tense agreement in indirect speech with little systematic investigation. Chaucer’s tense shift is similar to the tense shift from the past to the present in Japanese which is derivable from I-mode. The aim of this paper is to reconsider Chaucer’s tense shift based on this Japanese I-mode. We set up two research aims 1) to describe tense shift systematically; 2) to make clear factors to promote tense shift. We concluded that tense shift in Chaucer’s narrative text occurs through wide ranging units: one metrical line, one simple sentence, one compound sentence, one complex sentence (main clause + nominal clause, adjectival clause, or adverbial clause), and a stretch of discourse comprising dozens of sentences, and that this repeated shift is due to the synchronization between the subjectivity of cognition or the conceptualizer and the phenomena with added subfactors of orality and generic/gnomic implications. The interpretation of this remains to be further considered.