Without proper elite intervention, the Roman plebeians tended to be impressed by political appearances rather than the true nature of political deeds. Political appearances could cause the plebeians to shift to a different emotional condition which altered their previous judgment. Such an impressionistic mode of cognition of the Roman plebeians was an exploitable weakness for the Roman patricians. Knowing the plebeians’ limited judgement capability and susceptibility to appearances, the Roman patricians consciously manipulated political appearances to induce facilitative emotions in the plebeians to appease their dissatisfaction, disguise the patricians’ selfish acquisitions, and ensure the patricians’ ability to command. The patricians’ deceptive self-aggrandizement and a resultant widening politico-economic gap between the two classes could be hardly perceptible to the leaderless plebeians. The widened the politico-economic gap eventually ruptured Rome’s solidarity into catastrophic factions and civil wars in the late republican period. The plebeians’ tumults conveyed their indignation about patricians’ domination and rampant acquisition when inequality and injustice became palpable to them. Therefore, Machiavelli appreciates the patrician-plebeian contention whose proper intervention addresses the inequality, appeases plebeians’ indignation and prolongs the longevity of a republic like Rome. Machiavelli recommends mixed regimes to institutionalize plebeian democracy so that the patrician-plebeian disunion could contribute to their stability and perfection. The democratic institutions in a mixed regime effectively achieve an overdue reconciliation of political exploitation covered up by elites’ slyness. Because of the asymmetry of political prudence between the two classes, failure of elite intervention and political reconciliation is an ineluctable threat to a well-organized mixed regime even with institutionalized plebeian democracy. This paper attempts to delineate the “effectual truth” of the Roman plebeians’ passions and judgement to evaluate the compatibility of patrician political interventions and democratic institutions.