Abstract: Based on the Appraisal theory proposed by Martin and White, the present study focused on an American Parliamentary debate qualitatively, aiming to examine the cultivation of critical thinking through participation in parliamentary form of academic debate. It was found that based on the intersubjective stance stating the sources of voice and the undertaking of "subjective responsibility", Government and Opposition both adopt suitable Graduation and Attitude strategies to establish their own thesis, make a timely, accurate and forceful rebuttal and disagreement and justify their respective evidence for the purpose of reaching a common ground on the basis of eliminating disputes in a spiral form of movement threaded by constructive speech, rebuttal and justificatory response to opponent's POI.